Restoring Discourse 1.9 backup onto v2.3.0.beta9 +184

Downgrading isn’t supported, you can’t roll back to beta or stable until they pass the current tests-passed. You can use the commit ID as per this topic, but it’s very unlikely a routine upgrade is the cause - Discourse isn’t prone to spontaneous combustion.

Do you have sufficient free space on the server? Have you disabled all plugins and re-tried?