I've had my Model 3 for around 16 months. For the first year, maybe more, Bluetooth worked perfectly. Then, I traded in my previous iPhone for a 12 Pro Max and instantly started having issues. At least once a week the doors won't automatically unlock; I have to open the app and hit the unlock button. It will also prompt me to use the key card when I push the brake pedal. Such a pain in the butt when I'm carrying a bunch of things and my hands are full and the trunk won't open (I know, first world problems and all, lol).
Whenever this happens I simply turn off Bluetooth on my iPhone and then turn it back on, wait a minute, and then everything works normally again. That's the "easiest" fix I've found so far.
Another thing I noticed when I got the new phone is that I have to literally press my rear end against the trunk (I keep my phone in my back pocket) and hold it there for a couple of seconds for it to unlock.
And I know it's not just me or just my phone. My IT guy, who is amazing when it comes to things like this and knows everything about iPhones, Teslas, computers, etc. has the exact same problem, and it also started right after he traded in his old iPhone for a 12.
Long story short, IDK if this is an iPhone issue (which I'm leaning towards) or a Tesla issue but c'mon, it's been several months now, one of these companies needs to identify the issue and patch it up!