Hi Flomax!
Are you using KDE? Because I had this exact issue on Arch/KDE about two months ago and couldn’t find a solution either. I haven’t had the problem on Arch/GNOME or CachyOS/GNOME. I do use Clipboard-Indicator on GNOME, so perhaps that’s a factor.
Welcome aboard, and I hope this mystery gets solved soon. I remember it drove me nuts for a solid week before I gave up. 