For the record, yesterday I deleted all my listens & did a new import from Last.fm. I did that because I had a lot of duplicate listens due to some very early imports. I don’t remember how many listens I had before deleting them.
We just released a new version of ListenBrainz minutes ago. We switched over to a new data store that was mostly in sync with the old data store, except for if people had cleared out and re-imported their listens just as you did.
Do the delete/reimport again and all should be well.