Hi,
It looks like Opera Portable is not properly recognizing your session and tab files, likely due to corruption or version mismatches. Since it's generating new 0KB files, renaming old session files alone may not be enough. You can try opening the Tabs file in a text editor to check if it contains any readable URLs—if so, manually extracting and restoring them in Opera might be your best option. Additionally, using a tool like SQLite Browser (if the file is in SQLite format) could help retrieve lost data.
If Opera Portable doesn’t support direct session imports, another option is to try loading your files into a standard installed Opera version and then syncing tabs using an Opera account. Otherwise, consider restoring from a backup if you have one or using a recovery tool to extract lost browsing sessions.
Regards