Also having this issue. When it’s uploaded, verifies, and has the subsequent (504) error, if you go to ‘backups’ and restore the latest backup (a previous failed attempt at uploading), the chunks and player data is gone. However if you happen to use datapacks (Like I do) they work just fine. So somewhere in verification between ‘datapacks’ and ‘chunks' the whole thing breaks.
Also having this issue. When it’s uploaded, verifies, and has the subsequent (504) error, if you go to ‘backups’ and restore the latest backup (a previous failed attempt at uploading), the chunks and player data is gone. However if you happen to use datapacks (Like I do) they work just fine. So somewhere in verification between ‘datapacks’ and ‘chunks' the whole thing breaks.