https://www.teamfortress.tv/54707/any-activity-on-2nd-monitor-kills-fps-in-tf2#1

this may be relevant to you. The issue didn't go away after upgrading GPU for me, so its most likely a windows 10 thing

i was having a similar issue to that, my solution was switching from regular obs to streamlabs obs, which has all the twitch dashboard features integrated so u dont have to have the dashboard page open

You could try and set the affinity of the browser to not be on core 0, which tf2 loves, and see if that helps at all? I get major issues whenever I get a message on steam for some reason that seems like the same thing you're getting.

I enabled the hardware accelerated GPU scheduling but it didn't really fix it. I'm not sure if this is a thing but it seems to be that when I first start streaming my game feels pretty choppy unless I minimize the twitch window (or have another tab with something else like pugchamp) and then part way into the pug it feels smooth again randomly. I just built my new PC and am using windows 10 for the first time (was on windows 8 before), maybe there's more settings I should configure to get it to run well. Read somewhere to enable game mode in windows 10 so I have that too. Maybe there's some other optimizations I need to do first.

Specs are ryzen 5 3600xt with 3200mhz ram and RTX 2070 super which completely shreds tf2 when I'm not streaming and when it's acting normal (with twitch dashboard minimized). My CPU is only running at like 25% capacity usually and task manager says 4.25-4.3 ghz usually (default speed 3.8, max boost 4.5) but maybe there's a way to mess with the bios to get it to think it needs higher clock for tf2 to be happy lol. Checked the temps and it never went too high or anything, running on stock cooler. Could probably get a better cooler and overclock it if need be but I feel like this is an issue with twitch and/or windows 10. Just changed the affinity of chrome to not be on cpu 0, will see if that helps tomorrow.

whats the refresh rate of ur monitors?

It's a windows 10 issue. Any animation playing on your secondary monitor will limit the refresh rate of your primary monitor. As far as I know there's no fix for it, though I would LOVE to find one. As it is, windows is just being windows.

The same thing will happen if you have pugchamp open and your pre ready bar / ready up bar is ticking down.

Which browser are you using?

Disabled the Stream Preview video player in the dashboard? (Click the pencil right of Stream Manager to edit panels)

Using chrome, have the stream preview disabled, tried enabling and pausing it but same issue. I can have the OBS stream preview open on my other monitor too and it doesn't even add any lag (used to on my old PC it would feel way more laggy). I used to have my second monitor at 144hz with my old setup but the new one only has displayport/hdmi ports so I had to use the included displayport -> DVI adapter but from some googling it doesn't seem possible convert it to dual link DVI, so I guess I'll have to get a displayport cable if I want the second monitor to use its full refresh rate.

240hz main monitor, 60hz second monitor (unless I get a new displayport cable to use instead of the DVI-D). Would the windows 10 limiting refresh rate of your primary monitor go down to whatever the refresh rate of your second monitor is? I don't really mind having 60hz second monitor but it would be nice to have 144 and not have the potential of it doing this shit, or if it did limit it down to 144 sometimes that's not as big a deal.

I'm really hoping there's some fix for this, this seems like such a stupid bug people must've gotten around it somehow.

Edit: did some searching and looks like game mode causes problems so I'm going to try disabling it lol classic windows

Try updateing to Windows 10 2004 if not already. It fixes different monitor refresh rate issuses.

That should already be the version used:

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Does the framerate get impacted the same/less/more if you run TF2 in -window -borderless instead of -full?

Correct, that is the version I'm on. And not at about windowed borderless, will try it tomorrow. With the above changes it would still eat away at fps having the dashboard open, in a jump map it went from perfectly smooth literally over 800 fps to under 200 and feeling like the monitor was on 60hz (which would make sense given the refresh rate stuff people have been saying). Will try other brothers like Firefox today to see if it's just a chrome thing. Would rather not have to but another option dbk suggested was using streamlabs obs. Have all my stuff configured already and don't want to have to remake all my scenes and such. Also have automatic scene switcher plugin configured and don't know if that even works in streamlabs obs. Bttv is also nice to have which I don't think would work with it. Oddly enough the dashboard didn't always lag me, I would be able to use it sometimes and be fine but other times I'd have to minimize it the entire pug because it felt so bad with it open. Will try popout chat instead but think the animations are the issue. Maybe using IRC would fix the issue? I haven't disabled window aero visuals/animations yet because I thought they wouldn't have any effect due to me not moving the windows or minimizing them or anything (and I kind of like how they look) but will test it out to see if that fixes it too.

If it's just the chat and/or activity feed you need from the dashboard, you can add those popouts to your OBS window as custom docks (chat supports BTTV and/or FFZ there)

Will recommend against using SLOBS, but if you want to test, you can import scenes/settings between both versions.

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Additionally, there's GPU acceleration you can enable/disable in Chrome somewhere, if not Firefox, see if that changes anything, if using the twitch dashboard popout as OBS docks doesn't get the job done instead.

As an alternative to using the twitch dashboard I highly recommend Chatty.

It's lightweight but packed with features. You can admin your chat, change stream titles, change games etc with it.

https://chatty.github.io