My subscription ran out and I was at 17/6 characters. In the collections -> characters page some kind of a dialog box popped up about unlocking some characters. So I picked two, not really understanding what was going on.

The two I can now access, which is good. So now I deleted a bunch of characters and am at 5/6, but I cannot access the 3 characters that I didn't unlock. I don't really understand the reason why they would stay locked. Is there a way to unlock these as well now that I'm not over the character limit?

If you don’t pick the < 6 you actually want in that popup that you saw, they get stuck like that. You got two options:

1. Renew your subscription, even a single month of the Hero tier (cheapest possible option) is sufficient.
2. Contact support: (https://dndbeyond.zendesk.com/hc/en-us/requests/new?ticket_form_id=602788)

Thank you