I saw that error during the migration (after accessing the /setup URL) from the 9.4 to the 9.5 version, and from now on, every time I tried to start SonarQube (docker start) it failed with the org.sonar.server.exceptions.BadRequestException: Rule with UUID AX2_I9xF-Xhu6cui6fS_ not found error.
After digging more into this, I discovered that the the rules table was not behaving correctly (I couldn’t perform a simple select * from rules where uuid = ‘AX2_I9xF-Xhu6cui6fS_’ even though the row was there).
So, I ran a REINDEX on the rule table index and everything worked fine. I suspect that the initial error mergejoin input data is out of order was due to the index being corrupted.
Weirdest thing I’ve seen in months.