Quick answer: Unreal FastArraySerializer not replicating when the entire array is replaced? Replace = clear + add; fast array tracks per-item; full replace miss-tracked - use MarkArrayDirty.
Server: Items = newItems; clients see old items.
Call MarkArrayDirty
Items.MarkArrayDirty();Forces full re-replication.
Or clear and add
Clear; iterate new items; add each. Per-item dirty.
Audit replace patterns
Each TArray replacement: dirty marking needed.
“Fast array assumes per-item changes. Replaces need explicit dirty.”
If your replicated arrays are replaced wholesale, the MarkArrayDirty is mandatory.