I was having this issue with my sensors eventually decaying into a

maximum recursion depth exceeded in comparison

during a serialization process in dagster's code. (see here). This was on 1.2.7, i've recently bumped to later 1.3.7 and was still seeing the same issue (slight difference, the error from the code-location is now appropriately lifted up to the daemon so it's more directly observable from the sensor page). Any idea why this might still be happening, it seems to correspond to number of ticks, i.e. it scales inversely with the tick interval. Documented fully in the above thread, but to reiterate, after enough ticks the sensor will eventually get stuck in a failure state of

RecursionError: maximum recursion depth exceeded while getting the str of an object
  File "/.pyenv/versions/3.9.11/lib/python3.9/site-packages/dagster/_grpc/server.py", line 688, in ExternalSensorExecution
    serialized_sensor_data = serialize_value(
  File "/.pyenv/versions/3.9.11/lib/python3.9/site-packages/dagster/_serdes/serdes.py", line 609, in serialize_value
    packed_value = pack_value(val, whitelist_map=whitelist_map)
  File "/.pyenv/versions/3.9.11/lib/python3.9/site-packages/dagster/_serdes/serdes.py", line 656, in pack_value
    return _pack_value(val, whitelist_map=whitelist_map, descent_path=descent_path)
  File "/.pyenv/versions/3.9.11/lib/python3.9/site-packages/dagster/_serdes/serdes.py", line 690, in _pack_value
    return serializer.pack(cast(NamedTuple, val), whitelist_map, descent_path)
  File "/.pyenv/versions/3.9.11/lib/python3.9/site-packages/dagster/_serdes/serdes.py", line 524, in pack
    packed[storage_key] = _pack_value(
  File "/.pyenv/versions/3.9.11/lib/python3.9/site-packages/dagster/_serdes/serdes.py", line 690, in _pack_value
    return serializer.pack(cast(NamedTuple, val), whitelist_map, descent_path)

Which is "resolved" by just restarting the code-location service until it will eventually happen again

commented on the original post - if it's possible to share the code of the sensor hopefully that will help us get to the bottom of this