This was solved in a previous issue but now appears again with the 5.6.0 and 5.8.0 appimage (downloaded today). How to reproduce: Group some images, then drag & drop them into another folder. They will be ungrouped.
OK, this might in fact be a duplicate of #375703 - although this also happens with local albums, not just remote ones. Let's wait for the 5.8.0 release. *** This bug has been marked as a duplicate of bug 375703 ***
Not reproducible with 6.1.0 Gilles Caulier