Hi, so the change I was discussing with the dev team is different but turns out not to be related to the issue that you’re running into (it was related to how the CMC handles notifies). The CL for the change that I think you’re referencing is 38234235. That was an ASAN failure we were hitting in Fortnite server builds. The callstack for the failure was different, but that doesn’t mean it couldn’t be related, since it’s memory stomping. Do you know if the montage is blending out when the crash happens? That was the specific case that was failing without that change. I don’t see any harm in backporting that CL if you wanted to.
Apart from that, it’d be good to get any extra information that you have. You said you have a crash dump - does the entire Instance ptr (from Instance.Montage.MarkersPassedThisTick) look invalid in the dump? Are you able to get any other log data from the crash?