Greetings, and thanks for keeping us up to date.
It is possible to check the status of internal tracking issue 5556719? It is discussed in posts Fd leak with explicit sync and kde plasma - #30 by renari and following.
It results in sync_file descriptors being leaked every time a KDE taskbar tooltip appears, resulting in a crash and loss of all applications in normal work use for me. It may only happen with nVidia explicit sync enabled.