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" Does this behavior suggest the relays are fine? "

No, intermittent circuit connections are often agitated by vibration and/or heat. It could be the relay contacts or the solder joints and in a very rare occasion a defect or crack in the copper foil of the circuit board.

The relay is probably the issue, but solder joints fail too.

To bypass the relay. Turn off the power.

Remove the relay and insert a very thin wire (the thickness of the relay contact pin) into the socket OR in this case since I believe they are only using the NO contacts, if you can't find a thin enough wire to insert into the socket, carefully, securely rap a short piece of thermostat wire around the two relay pins up near the base of the relay (as illustrated below) and there should be enough of the pin left to make contact with the socket when the relay is re-inserted. The added wire should only touch the desires pins, touching the Coil pins would be bad since there is 120 VAC there !!!

Bottom view of the relay

The solder joints can be inspected rather easily. Turn off the power. Disconnect the thermostat wires, remove the nuts on the left side and gently squeeze the barb on the plastic stand-offs and lift the board just beyond the barb, when all the stand-off barbs are released the board can be raised off all the stand-offs and folded out with the AC wires attached. Or disconnect the AC wires too if that is easier for you. Inspect for cracked solder joints where the relay socket is soldered to the board.