When I interact with unreal 5.0.3 main menus or short menu the mouse become very laggy , is there a solution to this ? I tried disabled all startup apps but did not work.
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I’m having the same problems on both 5.03 & even 5.10 (Preview) versions.
I thought something’s going on for the UE installed from the Epic Games Launcher & decided to use the source version.
Same results still, every clicks on the Unreal Editor menu will cause this as well, even when there’s no shader compilations.
Can you share your specs? I’m using Ryzen 5 3600, Radeon RX 6900xt with 32GB of RAM, last time I was using nvidia & was able to use the engine just fine previously.
Were you guys able to find a solution? I’m also having the same issues. I have a radeon card as well but i just bought a 4090 so once that arrives i’ll see if it’s only an AMD issue
I think it is multimonitor problem. Using secondary monitor instead of primary solved the issue.
i just swapped out my rx 6700xt and put in the 4090 and unreal works smooth as butter now the issue is fixed for me
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but can it run solitaire ? 
we should all report this bug to AMD then
I’m using 21:9 ratio ultrawide monitor, yeah I think its because of scaling issue, as when I use the unreal editor in windowed mode instead of fullscreen no more mouse lag.
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I’m also using an ultrawide but even with my AMD card the issue was still happening with my second monitor. With the Nvidia card my ultrawide runs no problem. Maybe we’re experiencing a similar symptom of different problems.
Perhaps AMD’s issue then, as my last RTX2070 Super works fine too.
Try disabling Radeon anti lag. Fixed it for me.
Turning off Radeon anti-lag didn’t fix it for me. Turning off auto-hide on the windows 11 taskbar did though.
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I’m having this problem now and I feel like it started after GeForce driver update. My second screen doesn’t have any issues, but the main screen does.
Have same issue after installing 5.3.1. This is my first time playing with UE since many years ago. Installed fresh, got this mouse lag/menu flash thing. Set my side monitor as primary and then put UE in my middle monitor no longer set as primary and problem goes away. So, primary monitor bug. 
Found a fix for mouse lag on primary monitor; The issue (for me at least) seems to be related to having the UE editor maximized or in Fullscreen mode. Disabling Fullscreen mode and/or resizing my window manually caused the lag to go away.
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That is so weird… going off fullscreen fixes the lag for me aswell. Having the mouse lagging on the editor issue with UE 4.25.4 built from source. My guess is that it’s having issues utilizing my gpu (6700xt) cause it won’t go over 25% or so… Been messing with my gpu settings for a couple of days now. I once fixed it by enabling vsync but then there are some weird blacking out moments whenever I hover over settings… With the new drivers update as of yesterday vsync is not solving the mouse lagging part anymore but still has those weird screen blacking moments lol.
I’m on 5.3.2 and also just recently started again after a few years. But moving the editor to the second monitor or going off fullscreen mode all did not help 
This is really annoying to work with.
I’m using a i9 14900 and a nvidia 4070.
Same issue, … it fixes if I leave one of the windows (ie outliner) visible but in floatable windows mode… and do not minimize, it is very annoing but it works for me, also ( as somebody mentioned above) works if you use the editor in windows mode, not full screen (no need to have the outliner open in wondow floatable mode) … gygabyte radeon 6600 eagle, core i5 32G ram
I had this issue bad and a previous poster here had the correct solution for me.
Disable Auto Hiding the Taskbar