Trying to increase unreals actor movement replication to 3 decimals and overriding FRepMovement.
For debug I tried breakpoints, prints and logs in NetSerialize within my struct FRepMovementAdv and functions that are called from NetSerialize. No chance getting anything to work, as you decribed already. Gues those functions are called from another thread? But does it realy matter what thread it executes on in terms of breakpoints?