As per my update post in the migration thread from February all accounts were migrated then and any login issues seen after that point would be an indication that something went wrong. There are some backend work left to do which is the main reason the notice is there in the panel still, this Corona virus did further impact timeline for that however.
Between December 16th and May 21st you did not login to the account once, this lead it to be marked as inactive and purged in early March. The automated suspension system is halted during our maintenance, the login requirement (once every 30 days) has always been there however, so in mid of January the account would have been eligible for a suspension, and then 21 days later, first half of February it would have been terminated by the automated system.
Due to this being halted we did run a manual purge in early March (it was started the 4th) and since your account did not have any logins the the 60 days prior to the purge it was terminated as inactive.
Due to there being no warning emails as those are part of the automated, currently halted, system we said we'd this time allow for a restore if requested within reasonable time.
Initially we said cutoff for restores would be one week, meaning in reality we should not restore anyone past Sunday 15th, though we extended it a little bit extra, but it was said that the last cutoff date would be on Sunday March 22nd.
You're lucky though that the restore is still possible for your account.
I'm running the restore now and the account should be good to go in a few minutes.