General Help - Home Assistant OS won't boot 'headless'

I’ve been running Home Assistant OS on a raspberry pie 4 for over a year. About late November/early December (2024) a core update happened and HA wouldn’t start at all.

My first step to troubleshoot was to hookup a keyboard/monitor to see what went wrong and it booted fine. I took away the keyboard/monitor (head) and it won’t start/boot. I’ve done it several times (headless/non-headless).

My question is:

How do I trouble shoot a problem that only occurs headless and works fine when trouble shooting tools are in place?

(Yes, my HA is running with a keyboard/monitor attached to it because it’s better than doing without it, maybe, for a while?)

MrGrey.