New launcher (1.0.51) causing stutter on Windows systems [SOLVED]

More of a PSA considering I’m unsure Zwift even read this forum any more.

I don’t know if the recently publicised new launcher for Windows installs additional telemetry or something, but on several PC builds I have confirmed it to be the source of newly observed stutter in the game irrespective of circumstances or outright performance/frame rate.

All Windows 10 20H2, fully updated
All Nvidia driver branch version 45x.xx
All on latest version of Zwift game, installed with launcher 1.0.51
All running from SSD
All ethernet to 40Mbps broadband
All using full screen mode, as selected in the Zwift settings menu
System 1: GTX 1060 6GB to 1440p Gsync compatible monitor
System 2: GTX 1650 Super to 1440p Gsync compatible monitor
System 3: GTX 1050 Ti to 1080p 60Hz TV

On all systems, whether matching display refresh rate (TV/monitor) or below (Gsync monitor), the expected smooth motion was missing. Noticeable stutter was present at all times, in and outside of group events, when quiet and busy in terms of logged in numbers, on different worlds, and at different login times. Most easily seen by using camera view 9 overhead (the road beneath passing by very unevenly), watching other riders coming past in the opposite direction, and noting the motion of static objects passing by such as street lights etc.

Reinstalling the game from scratch with launcher 1.0.51 including clearing all files and rebooting made no difference.

Reinstalling the game from scratch using launcher 1.0.44 or 1.0.50 immediately restored the expected/normal smooth performance, without changing anything in Nvidia settings, Windows or display settings, or any other changes to the systems whatsoever.

Further testing shows that switching launchers as an in-place upgrade/downgrade (i.e. without full reinstall of the game) repeatedly introduces (1.0.51) and eliminates (1.0.50) the problem, so there’s something clearly not right with the current version. I’d therefore recommend Windows users stay on the previous launcher version rather than upgrading, for the best experience.


I asked our QA team, and we’d like to see your game logs and launcher logs. Would you follow the how-to on this support article and send them in?

There are a bunch of files called log.txt, log (old1-9).txt as well as Launcher_log.txt. We’d like to see everything in the logs folder, please. Thanks.

Sure, assuming you mean only logs with the new launcher installed? I’ll need to reinstall it.

Edit: no I won’t, got some from last night. Sent.

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The launcher app’s function is to kick off the game app, but should not change the game behavior.

We are aware of some issues that you are describing that are not related to the launcher version. There are two performance issues we are aware of that have emerged: an Nvidia driver related performance issue that is in the last game release, and occasional stuttering due to the larger player base and large events happening this month.

We are looking to address the first later this week, and we are testing a change to improve the stuttering in a future release.

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Thanks, as advised this is repeatable back to back in minutes with no changes whatsoever to the Nvidia driver or indeed anything else. Literally just the launcher version installed - old ones are fine, the new one is not. Same [latest] game version with both. It has happened at any time of day or night; both with fewer than 3,500 on Watopia and also when tens of thousands were online. I don’t recall the exact numbers, but it specifically wasn’t obviously linked to the numbers online*. I first noticed it after a clean install of Windows and Zwift with the new launcher on the GTX 1050 Ti system, then much more obviously when I did the same on the more powerful GTX 1060 system which should have been flawless.

After initially spending several hours trying to change different settings and graphics cards (and reinstalling Zwift) I realised the only thing different on the clean Windows installs was the launcher I had used. Swapped back to an old one and the issue was instantly gone, I then repeated this on the 1050 Ti system to confirm it worked, and it did. If I go back to the new launcher, the stutter comes back. Now that I know the game itself doesn’t need to be fully reinstalled to repeat this behaviour, it takes a matter of minutes to bring the stutter back or eliminate it. As the log file timings will show.

*I’ve just tested it again right now on a system with a GTX 1660 in it, exact same behaviour. Just over 8,000 online and testing carried out on Watopia with 3,500 online, so it seems detached from large user numbers.

I note the launchers extract a couple of DLL files and the new one includes a C++ Redistributable Package (presumably to resolve Bluetooth support issues), so perhaps the issue relates to one or more of those.

Anyway I hope this information is useful.


Would that be the source of the windowed mode vsync issues?

Bumping this to advise that not only is the issue with stutter originally mentioned still present, but a few of us have since discovered that it also introduces graphical anomalies at high frame rates with vsync off (for testing purposes). Riders rapidly disappear and reappear, whilst their bikes remain. Same sort of thing as seen on low end devices in big group events. This is on the very latest version of the game btw, and irrespective of Nvidia driver version etc.

As before, overwrite the launcher with 1.0.50 and this issue instantly goes away. Something is wrong with the files the updated launcher installs.


Bump. Please fix this given that using the old launcher has seemingly been killed.

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Can someone from zwift please acknowledge this issue.

It is clearly a problem as it is easily repeatable and has been shown to happen with multiple people.

It doesn’t affect me but I know Dave has been helping many others out and deserves at least the decency of someone from zwift replying to him.


They did sort of acknowledge it in the other thread I made when they started trying to enforce the update. Basically amounted to this:


All that’s going to happen now is that all the people happily running the old launcher will get a completely unhelpful error message and have to upgrade it to get Zwift running again (though the chances are they’ll end up reinstalling the whole game, which is great).

So everyone on decent systems with high refresh rate displays will be back to the flickering avatars etc, and it makes the experience noticably less smooth for me.


but Dave, they introduced two new wheel sets that are not any better than other options already in the game and that you probably don’t even need or want… how could you leave Zwift in such exciting times???


In fairness they appear to believe 30fps is the best Zwift has to offer, in which case literally none of this is a problem. Can’t see stutter or flickering if it’s crap all the time. :point_right: :woozy_face: :point_left:


@shooj any chance we can get the old installer on a box account like you did with the BLE file on the other thread?

that would at least acknowledge the problem and a workaround for us – and we wouldn’t have to bug dave for it all the time :slight_smile:

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It doesn’t work any more, that’s the problem. I have a copy of it but it can’t be used.

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curses. yah, i just saw your other thread :man_facepalming:

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Hey Zwift, I use a decent PC and get micro stutters with the new launchers, fix this please, this IS an issue!
Launcher 1.0.50 has a silky smooth framerate.


Adding my voice to this - been using the older launcher to fix the stutters since Dave originally identified the fix for us with half decent devices that we’ve built to take advantage of the Zwift capabilities - please sort asap.


Clean installed Windows 10 Pro and Zwift with a fresh copy from the website.

The game is a stuttering, flickering mess. Just as it was nine months ago with these launchers. Doesn’t anyone at Zwift run or test the game above 30fps? It’s a joke.

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Think that is all that was needed!

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You jest, but they must test it at some point.

But when you have senior game designers claiming that TVs only go to 30Hz, (exposing several aspects of misunderstanding) and the ludicrous tier of hardware required to consistently hold good frame rates on Makuri Islands, it makes you wonder if 30fps is the company’s target performance threshold. Which is roughly what you get from an Apple TV, though I’m sure that is just a huge coincidence. Meaning issues seen above 30fps are not seen or are not a concern, and complaints about smoothness going backwards fall on deaf ears.