I can confirm a large slowdown on the CharacterMovementComponent CPU times on 5.6.
When a character moves left/right the cpu time on 5.4 was at 0.14ms, on 5.6 gets to 0.20ms. which is 43% slower! I tried adjusting the net settings but it didnt improve performance at all.
To improve performance consider replacing the charMov class from one an older engine version