I had a problem with Android Auto: the car no longer wanted to connect properly to the phone, even after having a few quick attempts to fix it.
In the end I sorted it out by doing a bit of housekeeping directly on the smartphone. I went into the Android Auto app settings, cleared the cache and data, then removed the previous pairing and set it up again from scratch with the car.
After doing this the connection started working normally again. I’m writing this because it’s one of those trivial things, but when it happens it can waste quite a lot of time before you think of it.