A regression introduced in PostgreSQL minor releases 14.23, 15.18, and 16.14 (released May 14th) can cause a MultiXactOffsetSLRU deadlock during WAL replay, hanging streaming replication standbys or PITR instances. The bug is triggered when the primary runs an older minor release (Q4/2025 or earlier) while the standby is updated to the latest minor version — a common scenario given the recommended practice of updating standbys first. PostgreSQL 17 and 18 are unaffected. Workarounds include downgrading the standby to 14.22/15.17/16.13, applying the specific upstream patch if self-compiling, or waiting for the next scheduled minor releases targeted for August 13th. An out-of-band emergency release has been proposed but appears unlikely before the scheduled August releases.
