Using the Editor in Fullscreen mode on Linux causes it to freeze and occasionally lock up the computer. This freeze causes the various symptoms described in the Results field. In 4.21.2 (CL-4753647) this repro just causes an Ensure but that doesn't happen in 4.22.2 (CL-6574378) or 4.23 (CL-6662967). When testing on Windows with -vulkan, this repro causes the screen to flicker but it does not lock up or freeze. Logs are attached from each tested version. The terminal constantly outputs the following message when this freeze occurs: "LogRHI: Timed out while waiting for GPU to catch up on occlusion results. (0.5 s)"

This was reported and tested in 4.22.2 (CL-6574378). This was reproduced in 4.21.2 (CL-4753647) and Main 4.23 (CL-6662967).

Steps to Reproduce
  1. Open the UE4 Editor and create a Blank project
  2. Toggle Show FPS in the Editor and press Shift + F11 to toggle Fullscreen
  3. Move the mouse around the Editor and toggle Fullscreen a few times if needed

Results: The Editor locks up or freezes and sometimes can't be closed out or force closed. Mouse navigation becomes inaccurate in the Editor (hovering over an icon requires you moving a centimeter or so below it) and other programs like Google Chrome lose their mouse functionality from the Editor freeze.

Expected: The Editor to function as normal

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ComponentUE - Platform - Linux
Affects Versions4.
Target Fix4.22.3
Fix Commit6942703
Main Commit8614014
CreatedMay 29, 2019
ResolvedJun 11, 2019
UpdatedSep 20, 2019
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