We also started encountering this issue after upgrading to 5.3 and thankfully we found this thread early on. Thanks for documenting this here 
We tried to integrate the fix mentioned above but its kinda hard to add without considering “Chaos implicit object ref counted ptr” / TUniquePtr → TRefCountPtr change. Maybe there is an easy way to add this but we couldn’t see it.
We just applied the “workaround” CL that has since been superseded by the “proper” fix above. Easy to add and we didnt notice the additional memory cost associated with the workaround.