The Migrate H2 database from 1.x to 2.x and later document has a section "Revert your migration". It only refers to reverting the actual H2 database on-disk format change; however at least one customer has been confused and believe this is providing instruction for rolling back a Bitbucket version upgrade.

Bitbucket does not support downgrades, the only way to rollback an upgrade is to restore everything (database and filesystem) from backup. This document should be updated to clarify that the instructions are just for reverting the H2 on-disk format change and not for reverting the whole Bitbucket upgrade.