I have gotten this error using both MySQL & PostgreSQL and version 6 and 7 so don't waste your time trying everything like I did
Full PostgreSQL Error:
postgres_confluence | 2020-05-11 18:59:58.421 UTC [246] ERROR: duplicate key value violates unique constraint "unq_lwr_username" postgres_confluence | 2020-05-11 18:59:58.421 UTC [246] DETAIL: Key (lower_username)=() already exists. postgres_confluence | 2020-05-11 18:59:58.421 UTC [246] STATEMENT: insert into user_mapping (username, lower_username, user_key) values ($1, $2, $3) postgres_confluence | 2020-05-11 18:59:58.422 UTC [246] ERROR: current transaction is aborted, commands ignored until end of transaction block postgres_confluence | 2020-05-11 18:59:58.422 UTC [246] STATEMENT: select 1
Links:
https://jira.atlassian.com/browse/CONFCLOUD-62701
Fix... To Come.. Hopefully....