Cog crash during GC compaction (5.8b9)

 
Just encountered my first Crash in awhile, attached is the error log.

Not doing anything particularily interesting at that point, IIRC I was inspecting the WeakDependents, and had browsed a few Monticello repositories.

Sorry I can't provide any more details/have time to dig deeper into details up front this time :(

Cheers,
Henry