Unfortunately GSync is a pretty key piece of the puzzle too. I can go fullscreen until it is fixed (which will probably be alongside clubs, rowing, smart scale syncing, rankings based matchmaking, new UI and the ability to switch routes without swearing).
Also discovered this change today. I’m running on a 9400F/1660Ti, and usually get 60-100fps in Ultra depending on ride size. I’ve struggled to get 40fps since the update. Windowed or full-screen does not appear to have an effect. Setting vsync to “on” appears to lock it at 60fps. Note, that’s vsync, not G-sync.
So assuming you’re not using Gsync at all, it depends what setting you had before. Because the frame rate would have always capped at your display’s refresh rate (seems like 60Hz for you, so guessing it’s a TV) unless you specifically turned vsync off in the Nvidia control panel. The difference now is the behaviour when below 60fps, which is causing big knock-on problems for those using Gsync. Can’t say why you’re only getting 40fps on average, depends on the circumstances of those rides versus before. 40fps suggests group events or riding with a busy Pace Partner, in which case that happens to literally everyone.
To add another variant to this mystery: I’m using an Asus VP28UQGL 28" 4k 60hz gaming monitor, which supports AMD’s FreeSync tech, not Nvidia’s G-Sync. Key point on the difference between the two adaptive sync technologies:
One clear difference between Nvidia G-Sync and AMD FreeSync is how they handle graphics cards that produce higher frame rates than a monitor can handle. G-Sync locks frame rates to the upper limit of the monitor while FreeSync (with in-game Vsync turned off) will allow the graphics card to produce a higher frame rate. This introduces tearing, but also means that input lag is at an absolute minimum, which is important for twitch gamers such as those who play FPS titles.
Original setting:
- vsync disabled
- G-Sync enabled
- Running in window
- FPS: 60-100fps
New release test 1:
- vsync disabled
- G-Sync enabled
- Running in window
- FPS: 20-40fps
New release test 2:
- vsync disabled
- G-Sync disabled
- Running in-window
- FPS: either 30 or 60fps
New release test 3:
- vsync disabled
- G-Sync disabled
- Running full-screen
- FPS: 60-100fps
So, just another variant of the same issue: windowed mode now exhibits FPS throttling, but full screen does not.
I see a similar thing, frame rate in the recent rides is sitting at 30 FPS or very close to it. Remarkably, there are quite a few posts on NVIDIA forum where game ready drivers are discussed, in which similar issues are reported across a variety of games. It was also reported than downgrading to an older driver does not solve the issue. This makes one wonder if a recent Windows update may have created some sort of a conflict which is responsible for this behavior, rather than Zwift. Just a thought…
Freesync via Nvidia works perfectly well on most capable monitors, and is great for Zwift. I’ve been using it since it was launched in January 2019. 
But yeah it’s almost certain that your issues are the same problem.
Unfortunately it’s virtually impossible to tie these things back for certain, not least because Zwift uses OpenGL unlike basically any other modern game. So everything you see on forums, Reddit etc has to be taken with a massive pinch of salt as it very rarely relates directly to Zwift.
Nevertheless, there’s enough evidence that this issue did not arise on the latest version of Windows 20H2, nor old or new Nvidia drivers, prior to the latest Zwift game update (which incidentally was released more recently than even the latest 20H2 update).
So I did a fair few tests yesterday, riding with Coco Cadence, and then watching someone in the pack for a few minutes. All tests done in windowed mode. No matter what I set vsync to, very quickly I got “capped” at 21 FPS, this is with a RTX 2060 and Ryze 3 @ 4.1ghz.
I turned gsync off and min “improved” 
to 31still in windowed mode.
Ran full screen, min now 40
PS anyone know how many posts before I can post images??
Tested on a machine that did not have the 20H2 update and was running old Nvidia drivers. Same vsync issue.
The 20 year Quake2 uses opengl and happily obeys gsync, vsync or whatever Nvidia setting is applied on both machines.
I always keep the in-game FPS counter on, so my activity screenshots serve as a record of when the change occurred. On 11/22, it shows 106.4fps. Game update 1.0.58982 was released on 11/23. My next activity was 11/27, and I haven’t seen above 60fps since then.
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That matches what others have seen, whatever they’ve changed in this latest release is introducing additional (and often inexplicable) vsync behaviours in windowed mode. For you it’s capping at your display’s refresh rate of 60Hz. That’s actually what gives the best experience IMO, but if you simply want the maximum possible frame rate at all times irrespective of tearing then yeah it’ll be an obvious step down.
Windowed mode. Meetup - Keep together - Don’t show other riders. London.
Graphics drop for no apparent reason.
This is a old log file.
Meetup in the jungle showing all riders.
First one is classic vsync on behaviour; when you dip below 60fps it drops all the way to 30fps to prevent tearing. When it can maintain 60fps it goes back up again. These transitions introduce judder, but no tearing. This is traditionally what Zwift used to do if you left the Nvidia settings completely default, but you could get around it by enabling triple buffering (as per your second image) which allowed minor frame rate drops without tearing.
Since the last update, in full screen mode the default settings no longer have the hard drops to 30fps. The frame rate is now allowed to drop to say 55fps, albeit with tearing. This is why I think they’ve changed the default behaviour within the engine, from vsync on to adaptive vsync (which is a different thing to actual adaptive sync, such as Freesync/Gsync).
In windowed mode however you’re now getting vsync enforced (possibly by Windows itself), and this is conflicting with whatever the game is trying to do. When Freesync/Gsync is added into the mix, it’s even worse.
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Interestingly the Nvidia settings are the same for both rides. Also both in windowed mode using Borderless gaming.
Yep, so the change is within whatever Zwift have done. You’re now getting conflicting vsync behaviours despite not changing any settings.
In summary, as far as I can tell:
- Full screen mode with a TV or fixed refresh rate monitor works as before, but requires slightly amended Nvidia tweaks to avoid newly observed tearing.
- Full screen mode with Gsync/Freesync works as before with no changes necessary.
- Windowed mode with a TV or fixed refresh rate monitor appears to be having new vsync issues.
- Windowed mode with Gsync/Freesync is now a disaster.
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Lol. I guess I’ll resign to switching to fullscreen.
Dave, for all of us using Nvidia (mine is a GTX 1650) and being no experts - could you please list the settings for the best performance?
I know, it depends - using TV, monitor, HD, 4K…
But are there some common settings which should be made, when starting with nvidia default?
Thank you, ride on!
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RTX 2060 here. Latest updates/drivers. I’m usually at 60fps and today it almost a flatlined bang-on 30fps when riding with a Pace Partner bunch. Are they throttling FPS based on how many riders are on screen? Strange.
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I was playing around with # of riders in the Giant group ride today - when in the 50~75+ group size (guessing) around the beacon, flatline at 30fps, go off front or back with dozen or so, back to hard 60fps. Get the high quantity of riders on either side of road, flatline to 30fps again. Not sure what the threshold is but consistent with behavior of the Focus ride in the weekend as well.
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Windowed mode on a TV I believe? Since the update, old-fashioned vsync appears to be kicking in for users on that setup.