The event must be replicated to the server, try the top of the command line because the rest will also be, if it is associated with a blueprint, the variables must be replicated and the non-replicated events should call the replicates.
Have you set bReplicates = true; on the AStatusEffect actor?
I suspect it is an access violation crash meaning that LastAppliedEffect is NULL on the clients and the actor not replicating could cause that.
Found out that it just does not with my PC, but i have tried it on another PC, and there it works. I have deleted intermediate, binaries and saved folder with no change.
Are there more caches/settings that i should look for? Maybe i should reinstall ue4?