The conditions for this bug are fairly specific. The actor must be statically placed, with its only replicated property being the fast array, and net.PushModelSkipUndirtiedFastArrays must be enabled. The first time a PIE session is started, the array will be replicated as expected. However, on subsequent PIE sessions, changes to the array will only be replicated after garbage collection occurs. This bug doesn't occur in standalone editor instances, and the fix for [Link Removed] does not resolve the issue.
See linked UDN for more info, including detailed repro steps and sample project
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-164321 in the post.