Sorry but Smooth Sync just isn’t really designed to work this way. You can get away with changing some settings at runtime but others need to be set at the start and can’t be changed. Interpolation Back Time and Send Rate really can’t be sanely changed at runtime, or at the very least you should make sure they have sane values at the start as they are used to calculate the buffer size for storing states.
These settings can be changed at runtime on the controlling client (or the server if not client controlled):
Send Rate**
Send Position Threshold
Send Rotation Threshold
Send Scale Threshold
Send Velocity Threshold
Send Angular Velocity Threshold
At Rest Position Threshold
At Rest Rotation Threshold
And these settings are used only on the non-controlling clients:
Interpolation Back Time**
Time Smoothing
Position Lerp Speed
Rotation Lerp Speed
Scale Lerp Speed
All the extrapolation settings
Received Position Threshold
Received Rotation Threshold
Position Snap Threshold
Rotation Snap Threshold
Scale Snap Threshold
Things you definitely should not change at runtime:
Any of the Sync Modes
Is Using Origin Rebasing
Always Send Origin
Sync Ownership Change
** Not really sure about these, change at runtime at your own risk. Make sure values are sane (not 0) at start.