I exported my LastPass file then tried to import to BitWarden and got file format failure. After research I found that the folders (grouping) column would not import. I imported to Numbers for easier editing (delete folders column & other non used characters, also for some reason my export created 3 entries for every item, lots of work). I then exported the Numbers file to a CVS file and still got file format failure. After investigation I found that Numbers enters the file name on the first line of the CVS file, I deleted the line and the import to BitWarden worked. Hope this helps others.
Frank
If that was your 3rd export in the same LP session then that is expected. There’s a bug in the LP exporter. Start a new LP session for each export.
HTH 
Interesting, issues like that should never exist. Thanks for the reply, I got my file fixed, just had to spend an evening deleting rows.
After investigation I found that Numbers enters the file name on the first line of the CVS file, I deleted the line and the import to BitWarden worked
Just copying your answer so I can mark it as resolved 