Sorry for the trouble, the issue was found to be that the 4.10 project had a max concurrency count of 0 (which it shouldn’t have been allowed). When loaded in 4.11, the code which translates the old max concurrency feature to the new feature didn’t clamp the value of the old data to the proper ranges (i.e. greater than 0). The new system (correctly) asserts that there shouldn’t be a max concurrency count of 0 since that should mean that no sound would be allowed to play.
I submitted the fix to our 4.11.2 hotfix branch so it should come out soon. In the meantime, to fix the issue, either make sure your 4.10 projects don’t set a max concurrency of 0 before upgrading or add the following code change to your 4.11 solution in SoundBase.cpp in USoundBase::PostLoad():
ConcurrencyOverrides.MaxCount = FMath::Max(MaxConcurrentPlayCount_DEPRECATED, 1);