All of them are already set to Manual 100Mb/Full so no option of smart speed available.
Multiple units affected one by one. We are trying out FW upgrade of the SMs if that helps.
smart speed is not tied to the actual port speed or only available with automatic speed setting, it is a power state technology that reduces ethernet transmit power levels to keep the speed of the link stable but use the least amount of power to do so. Both devices MUST have nearly identical implementations of this feature to work properly.
try setting to disable first and monitor the results.