I'm in no way saying that plane jane CAT cable within a conduit is a good idea, but hell, there's plenty of places in New England where this exact setup/wire has been used for years and years without issues. Just walked a job the other day where they had 24 Cat5 cables within a plastic conduit, between buildings, for the past 18 years without issue.

My guess would be critters have chewed the cable to a point where you are getting intermittent connectivity or exposed wires within the water.

Sounds like a new cable is going to be needed to get this working again if the devices aren't faulty.