EDIT: Coincidentally, I turned off prevent cross-site tracking, because I got sick of raindrop.io signing me out constantly. However, that seemed, I think, to have solved this issue. The only other thing I changed was to turn on the compact tabs view, but I don’t see how that possibly could have had any effect on this whatsoever. So I think maybe the cross-site tracking prevention thing is broken, or something along those lines
Well, I’m glad it’s not just me. Although I’m also not that glad that this sounding like it’s widespread, and apparently Apple is either not aware of this or has not acknowledged it in any way, and does not seem to be working on offering any solutions at this point in time.