Most likely a gpu reset on SteamVR's side.
Related: https://github.com/ValveSoftware/SteamVR-for-Linux/issues/183#issuecomment-506684827
Why would such a reset break the ui of another application?
The reset isn't just resetting something from the SteamVR software but it resets the whole GPU driver. That affects all applications, some textures can be broken etc.
I haven't had this issue for a couple of months now.
Nothing extracted yet.
Your system information
Please describe your issue in as much detail as possible:
The client ui becomes illegible after closing steamvr sometimes. Random icons, text and backgrounds are replaced with stretched out versions of profile pictures of friends. Both the main window and some hover over texts are affected. This could be specific to video card drivers (gtx 1080, version 435.21)

Pictures speak a thousand words:
Steps for reproducing this issue: