@pmusaraj I checked this against Rails 8.0.5.1 and 8.1.3.1. A compatibility entry shouldn’t be needed: the corrected association works on both versions. The previous declaration fails to load on Rails 8.1 because it specifies class_name alongside polymorphic: true.
The initial report was posted about ~15 minutes before the fix merged, so it could have been from a rebuild without the fix.
@Jagster @satonotdead could you try rebuilding again with ActivityPub enabled? If you still get a 502, please share error log from /logs.