Enabling Allow Client Side Navigation results in a NavMesh Needs To Be Rebuilt error message on the Client

Enabling Allow Client Side Navigation results in a NavMesh Needs To Be Rebuilt error message on the Client. The Client cannot use the nav mesh.

This is a regression: this did not occur in 4.9.2 (though there appears to be a separate issue with it in 4.9). Reproduced in 4.10.0 binary. Did NOT reproduce in Main (CL# 2785572)

1. Create a new Top Down template project
2. Project Settings > Navigation System > enable Allow Client Side Navigation
3. PIE with 2 players

Result:
On the Client, "NAVMESH NEEDS TO BE REBUILT" appears. The Simple Move To used in the PlayerController does nothing (works in 4.9.2, though with some problems).

4.10 regression, client side navmesh seems broken