Ok, This bug is way too intermittent to debug by a process of elimination. It was 3 days before i did it again and then it did it several times in a row & now its not doing it again.
I did get a slim chance to try turning a couple of things off. I found that when i switched off firefox (which was on youtube with a video window open (but not playing)) It seemed to allow it to sleep again, although it may just have been a coincidence.
More interesting i have found several urls of importance, the main one is here
I have been trying to follow but its going to take another few weeks of learning as its mostly way over my head.
Anyhow, i have currently set my kernel back to 54 (the last LTS), it will take a week or so to see if its going to help or not.
I am likely to have many questions about the site i linked above though.
Where do i put these “arguments” ?
e.g. Adding the
initcall_debug boot option to the kernel cmdline will trace initcalls and the driver pm callbacks during boot, suspend, and resume
Where do look for their output? (will it be in the journalctl somewhere?).
I shall keep plodding onwards.