It seems there is the same issue at:
https://meta.discourse.org/t/postgresql-12-update/151236/298?u=lucasbasquerotto
There’s not an answer to this specific issue tough, in the FAQ, but maybe the discourse team add a solution to that, considering that more than 1 person faced it. There is a FAQ about The source cluster was not shut down cleanly, that could be related to your issue.