New launcher (1.0.51) causing stutter on Windows systems

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.