How to debug API connection?

I have an Atom S3 Lite with RS485 adapter which worked flawlessly for many months. Yesterday, all of a sudden it stopped working.

After some some time I could it get to ping at least when using an external USB-C supply (as opposed to the 12V from RS485 interface).

However, all its entities are still Unavailable. I can see the logs over wifi and I can re-flash via ESPhome. Yet, all entities remain grey and “Unavailable”. I tried to comment out all custom ones and only leave the Uptime sensor but even that one fails.

What could be going on here?

How can I confirm what is wrong with the API?

No logs = no issue

But no logs & not working == issue

Having said that, it really seems there was an issue. Reboot on f HA (!!) seems to have fixed it.