Diagonal lines in picture

Found a potential bug in Photoshop/Bridge, never encountered this before. I recently developed 6 portrait photos in Camera RAW. I then imported them into Photoshop (23.5.1) and did some retouching and saved them out as .PSD files. When I checked them in Bridge I discovered that four of them had two diagonal lines in the thumbs, always at the same positions, see attached picture.

At first I thought maybe it had something to do with my new Canon R6 camera, haven't used it much. But the RAW files have no trace of the lines, they only show up in the .PSD thumbnails inside of Bridge. If I view the .PSD files using XnViewMP there's no trace of the lines either. If I open the files in Phoshop, same thing; no lines.

I also get the lines if I use the Bridge Export function to save out the pictures. But if I use the Image Processor; no lines! Initially I suspected it might have to do with the flattened layer created by "Maximize Compatibility". But I assume that Bridge Export doesn't use that for export. Also, in that case the lines should have shown up in the thumbs in XNViewMp, which they don't. So has anyone encountered this before? So far it has only happened to the four pictures that I developed this week...

'