Just an update - I had the fan cover off yesterday and it was absolutely clogged with compacted lint. Pulled out as much, if not more than Iain's pictures above!! Quite alarming at how compacted it was between the blades. Also took the duct cover off as much as I could and it didn't look quite as bad but annoyingly the sensors triggered yesterday during a test run. This morning I had it apart yet again and cleaned up the duct (where the sensors are specifically) and also ran the "Fluff Clean" cycle on cold, which admittedly I had probably not ran anywhere near as often enough previously (knowing what I now know) AND ran an empty wash cycle with some washing machine cleaner in. It's currently drying 1/4 of what was on the wash cycle (decent sun today so most stuff went on the line). Fingers crossed, otherwise I'm kind of out of ideas. Unless triggering and resetting the sensors so much has made them prone to trigger more easily? Is that a thing?
Perhaps running the Fluff Clean cycle more often is key to solving this? It doesn't stress in the manual that it's even necessary, only to run it when drying cycles aren't working as they should.