Hi @djbill, welcome to the forum!
Can you confirm you’re getting the same “stuck on ‘completing backup’” situation that @Ivan reported?
It looks like @warwickmm, @kenkendk, and @Pectojin have all updated the MegaBackend.cs code in the last 6 months - but if you haven’t done any updates it seems like you are correct that they have made a change at their end.
Just out of curiosity, does the “test destination” feature still work? Also, if you create a small test backup (just a few files) to mega.nz does that work?