I have the same issue, and maybe a workaround for you. I already contacted Samsung Service as well but they mentioned it should be a single issue only. :-( and should contact a service center.
However, here my workaround:
Go to the phone app, switch to the digit keyboard and type/dial *#0*#
Now you are in the service menu. Choice "sensors" and check the first entry accelerometer .
When you see the digits changing then your sensor is working. When they are not changing, your sensor hangs. Click on the "graph" button, you will see a flat line, because the sensor hangs. Double wish from up to down on the clock screen you will come back to the sensor menu, but suddenly the sensor is working again. This happened to my gear s2. The issue is this way will not resolve the issue. E.g. When you sync with S Health the Sensor hangs again und you need to restart the procedure.