Your boards likely were moved into a Workspace:
https://help.trello.com/article/1263-moving-to-workspaces
And you had more than 10, so the least active boards were closed (not deleted).
https://help.trello.com/article/781-reopening-a-closed-board
Welcome to the Atlassian Community!
Trello still has a free plan, and that is probably never going away. See https://trello.com/en/pricing for the options and comparison.
For your boards disappearing, that's a totally different question. We need to know what has changed - your login maybe, or has someone claimed your Atlassian account that you were using for Trello. You say "lots", is that all your boards, or just some? Is there a pattern to which boards have gone?
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.