@operator777 I am facing a similar behaviour with my Opera browser as you describe. Maybe at the same time you reported this, I noticed missing passwords, with some 98 passwords still showing up in password manager, and the rest of it (maybe 100 or more) disappeared. Some investigation of the remaining passwords let me suspect, these are all old password recordings, with all the newer passwords having gone. Might this match to your experience?
I run Opera Next 95, it tells me I am up to date, latest version available. Login Data file is 924 KB of size.
I wonder, might the data be still available in the file, with Opera being unable to show it for some reason?