Just had a thought and wanted some clarification, do you mean this:
or this:
The former is the Security Indicator Light while the latter is the KEY Warning Indication/Warning Light.
From your initial description I thought you meant the latter but I wanted to check. The manual does mention the scenario I believe you are seeing:
If the KEY warning light (red) illuminates, or the push button start indicator light (amber) flashes, this could indicate a problem with the engine starting system. This may prevent the engine from starting or from switching the ignition to ACC or ON.
It then goes on to state:
Have you tried the following:
- Disconnect the battery
- Confirm the battery has a decent voltage with a multimeter (or battery charger) while disconnected from the car
- Reconnect the battery
- Retry starting
I have seen mention online of a faulty sensor draining the battery.
And if you have been testing with both keys please ensure there is only ever one actually in the car as it might have a tantrum.
Finally, can you find any other issues that also occur?
So far you have mentioned the infotainment system settings and boot alarm behaviour and I have also seen posts about the interior light.
When this happens, what else doesn’t appear to be functional?
I ask as I had some “fun” with my car where a whole series of different aspects failed but knowing them all I could trace them to a single origin (a certain computer).
And finally, finally, it could be the the starter relay or main fuse causing the issue. Have you checked these?
Thinking about it, I am leaning towards the starter/alternator side of the main fuse having gone.