Volvo V60 alarm/immobilizer issue

Throwing a Hail Mary here:

2017 V60 with the 4 cylinder motor.
Went out to load my gym bag this morning, I touched the hatch release and my alarm went off.

Key fob did nothing, I opened the door manually and even put the fob into the dash to try and stop the alarm, didn't work.
Car wouldn't start or even go into accessory mode.

In desperation, I ended up disconnecting the 12v battery, took another 3-4 minutes for the alarm to finally stop. I waited a few minutes, reconnected it, the alarm started back up again but this time it responded to my key. Car started up normally, drives fine with no error codes.

Full disclosure: I let the secondary start/stop battery die and I've been driving with it inactive for over 3 years. I've had zero issues during that time, except for the inability to leave the radio playing while the car is off. I tested the 12v battery and the key fob batteries, both are fine.

The last few days before this alarm issue, I noticed the garage door opener in the visor stopped working. No idea if those are related, just trying to figure out what would cause the alarm to trigger randomly...

First thing I would do is check the 12v battery. Low voltage can do weird stuff in modern cars.

Too new a model to work with the readily available versions of VIDA, but if you have access to a good scanner, see if you can interrogate the modules involved. There may be information buried in there that would be helpful in diagnosing the problem.

12v is 90 days old, I'd be shocked if it was bad, but it's worth a check

Volvos will inevitably have a laundry list of codes in every module, and most will be a one time set.

I'd worry about it the second time it happens.