I particularly notice this in IntelliJ, where I'm constantly cutting & pasting when refactoring code. It works perhaps 80% of the time, but in the remaining 20% the clipboard content goes missing. This is specifically associated with running under wayland, as IntelliJ cut/paste is rock solid under X. I will update this ticket if I noticed it under other applications.
*** This bug has been marked as a duplicate of bug 433854 ***
Do you have your clipboard history size set up 1 by any chance? If so this is Bug 466041 which was just fixed for Plasma 5.27.3. If not, please change the status to REPORTED if you can still reproduce the issue in Plasma 5.27.2 or later. Thanks a lot!