Finally got this solved, thanks to Tech Note: Replicated TArray Repnotify Not Being Called
If Unreal thinks that variable wasn’t changed, it won’t call RepNotify, even though it was explicitly called (Set w/Notify). This is not a quite obvious concept, but ok.
In my case the name I passed was not equal to ones in the array, so array would be just the same as previous => structure too => no RepNotify. After I fixed that bug, it started calling repnotify.
Issue on BugTracker: UE-119459