I had 3rd party video addons for PlutoTV, Stirr, Plex and Samsung TV plus, which bumped up my TV channel list to over a thousand channels as well as the TV guide via the Merge IPTV addon.
Anyway removing most of these from the TV Channel list and TV Guide has improved performance (most were crap anyway).
I suspect the constant TV guide updates in the background were the culprit, with so many channels and TV guide data to ingest.
For what's its worth I've reverted back to booting natively off micro ssd again and so far so good. Marking as resolved