This sounds like an intermittent connection problem. Something's loose or worn out of spec. Some of these systems use a relay to control the antenna, so that could be a place to look: the more connections, the more places to have problems.

Sometimes, you can get lucky and find something by just looking at everything and gently pulling or pushing to find a loose connector, corroded terminal, or 'barely hanging on' wire.

Don't be afraid to look for the easy, obvious problem. Sometimes that's the solution. Reseating a loose connection before replacing a good unit on suspicion. I've seen way too much of that over the years. The process is called 'Easter Egging', and is a mark of a bad tech.

How can you tell a ######## field engineer with a flat tire?
He's the one changing one tire at a time until he finds the right one.
(Old computer industry joke)

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