i am looking for other players that have the same or similar problems for the last few patches:
1) Game randomly just quits or crashes but you can reconnect afterwards.
2) You never had this problem before they implemented the new anti-cheat stuff a few patches ago. ( see https://boards.na.leagueoflegends.com/en/c/bug-report/GX3Zhxwe-game-client-anti-cheat-known-issues-and-fixes )
I also have a support ticket open, where they confirm that it is a problem with their new anti-cheat system.
By now i did a full repair, complete reinstall, memtest, disktest, OStest.
At this point i strongly suspect there is a problem with the new anti-cheat stuff Riot implemented a few patches ago that mostly affects lesser used OS(for example WinXP like me)/Hardware.
If you have this problem please comment here and if you can generate a dumpfile please do link it here.