I had the same Sync 3 in my ST before my RS in the ST it was fine but in the RS it kept dropping the signal.
After the APIM was changed, the aerial base itself was changed, the wire from the aerial unit to the APIM was changed and guess what no difference. Raised issue with Ford themselves and took them 2 years to get all that done to say ” we can’t seem to fix it “.
It would work fine after the dealer reinstalled the Sync 3 software for around 3 weeks but then it would come back intermittently failing.
It really annoyed the S**t out of me especially on a long drive but found if it played up stop the car turn it off open the drivers door then wait 30 secs and then it would work fine
Good luck though
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