Old thread, but FWIW I just now had a pretty good experience with Garmin, when I feared the worst, so here’s my .02.
Trusty Edge 520, nearly 4 years old, no problems (except the clunky UI everybody knows about), until started disconnecting / reconnecting phone and sensors repeatedly every few minutes on outside rides. It did it almost ritualistically so I I assumed it was a software problem in the 13.20 update.
First support chat, they suspected corrupt files and suggested deleting 4 of them from their folders. Didn’t help. Second chat they had me forget all sensors except the Varia radar (the only dangerous disconnect, since when connected it never gives a false negative, but does on these 10-30 sec disconnects). The radar still rhythmically disconnected as before. Third time I got a guy who stuck with me to resolution. At first he laid out a troubleshooting regimen that involved a couple test rides with Ant+ logging. I was curious enough to assent, even though it was kind of a pain.
He called later in the day to report that the engineers weren’t planning to support the 520 any longer, and didn’t want to investigate the testing, but I could get a 20% discount on any newer Garmin head unit. Of course I went into research mode on 530 vs Bolt everywhere I could, starting here. Hadn’t made up my mind over weekend when he called again first thing Monday and said they had decided to send me a refurbished 520 in exchange for my ailing 520.
It arrived 4 days later, and worked fine with all my sensors and phone – 9 days after first contact, 6 days after contact with the guy who could do something more than offer boilerplate suggestions. For a unit that old, it seems to me more than a fair resolution though it took some faffing around before getting there.