with seat switches being as they are, they can be inconsistant
just doing a general continuity check may not be good enough.

as a temporary test try bypassing the circuit at the harness connector under the hood and see if that makes any difference to rule out the seat switch being intermittent.
the seat belt circuit will have no effect on travel or lift on the OPS system, it generally just sets off a seat belt alarm or lights up an indicator on the dash if not buckled up.