Hi @AdhDyslexie!
So we can get some more insight, would you mind sharing the portion of your blueprints that call the player damage event and/or handle replication?
In the meantime, here is some live training that directly addresses health in a network multiplayer environment as a possible solution or insight into your issue:
Network Multiplayer Fundamentals | Live from HQ | Inside Unreal
Any additional information you can provide will be a big help!