I’m using kwin 6.3.4-4 on Garuda Linux (arch) and I’ve experienced a kwin crash after waking my box from suspend-mode, then pulling the USB-plug to my docking-station. After the crash kwin restarted and came up without screen-lock. It only happened once and I could not reproduce it and I don’t have a proper backtrace with debug-symbols available.
Hi! If you do end up being able to reproduce the crash, the steps here can help you collect a helpful backtrace for developers to investigate 
Guidelines and HOWTOs/Debugging/How to create useful crash reports - KDE Community Wiki