I FOUND AN 8 YEARS OLD XORG BUG

Summary from the TLDR Web Dev newsletter

This developer discovered an 8-year-old bug in Xorg (the open-source implementation of the X Window System display server), where windows would disappear even while the server was locked using the GrabServer command. The bug was tracked down using eBPF and uprobe, which revealed that it was a simple misuse of epoll that caused the server to process close-downs even when it shouldn't. This bug likely went unnoticed for so long because only compositors like picom need to know about all windows, but don't have control over their closure, putting them in a unique situation where the GrabServer lock is necessary.