A correction to above: if a states electoral vote is disputed, both the House and Senate needs to vote on the dispute.
Another possibility: if Republicans control the state where the unfaithful elector failed to vote for Trump as he should, the state itself could find a mechanism to nevertheless certify their full electoral vote for Trump, despite the unfaithful vote, before sending the certified results to Congress. At least some states have a law that they can replace an unfaithful elector immediately if he doesn’t vote as he pledged, with another elector who will. Other states might be able to do the same even without such a specific State law.