Do first gen BMW ‘smart’ keys fail?

[Magnesiumnitrate]

This one is a head scratcher.

2010 E70 3.0

Comfort access

Key fob just stopped working wirelessly one day. No spare to compare to.

Occasionally the fob works. Out of habit today I clicked it waking out and it beeped at me. Then nothing.

Tried:

Changing the battery.

Doing the resync procedure (start in dash slot)

Tested:

No faults in the CAS ECU.

ISTA shows key #2 in the dash.

When checking the battery levels ISTA shows transmitter #3 as discharging but 1-2 and 4-10 as ‘okay’

ISTA shows a field signal strength of 0.

Theories:

Key lost CA/Central Locking programming somehow. It thinks it’s key 1 but the car sees it as key 2.

Key has a bad capacitor, occasionally enough power to transmit is obtained but most of the time it’s effectively dead. (Shot in the dark, no idea how these specific keys work)

*tinfoil hat*

Previous owner lost a key inside the vehicle, and it’s slowly dying and DDoSing the CAS system with battery status. (Key #3 ‘discharging’)


Questions:

Would a bad passive go module or diversity antenna/amp cause these symptoms without throwing ECU faults?

Are there any other common failure points that may cause these symptoms?

The fact that I’m not getting anything in ISTA except green boxes leads me to believe it very well may be an issue with the key. What are my options at the dealer? Is it possible the key just needs reprogramming?