Car infotainment systems were designed around a small number of paired phones — often five or six — and they rarely tell you when that list is full. New pairings then fail or silently replace an old one.
Cars also treat calls and media as separate services. A phone can be connected for hands-free calling while media playback stays with the radio, which feels like the connection is half-broken.
Start-up order matters more in cars than anywhere else. If the head unit powers up before the phone finishes waking, it may connect only the call profile.
Software on the car side updates rarely, so a phone update can break a pairing that worked for years until you delete and re-create it.