A couple of times recently I had a window pop up saying "Warning unsafe paste" that showed me the contents of the copy buffer, I haven't seen it before. So I ran xwininfo and xprop -id xxxx to find out where it came from, and it was the XFCE4 terminal. So then I went to the terminal preferences and found a check box where I could turn it off. I don't know if it's a new feature or just got more sensitive, but if anyone wanted to stop it, that's how.
I just went and registered with this site -- I don't even use Artix! -- to thank you. It was driving me bonkers!
Glad it was helpful for you, I thought much the same ;D