I've been having this problem for as long as I am subscriped to the photography plan:
No matter what i try, when preparing a slideshow with a set of my pictures I always notice that some of the pictures (not necessarily the same all the time!) do not have there strobeborder sized around their borders correctly, instead they show up somewhere within the picture. It only shows up when I start the slideshow preview, press the play or export it (pdf or video), not in the active window where I prepare the slideshow.
So, whilst preparing it all seems ok but as soon as it starts rendering the slideshow it seems that for some pictures it can't correctly define that strobborder.
As it is hard to describe in words (english is not my native language) I've added a still from an exported slideshow (video, mp4) showing the problem right on the first slide.
I con't figure out what to change to get around this (the slides which are corrupted are not in a lower resolution than the others which do render correctly - it really feels like a bug in the slideshow module of LrC to me).
FYI: this is on a Macbook Pro i9 16" w. 1TB/32GB using the very latest MacOS (Ventura).
Any tips/advise on how to get around this would be welcomed.