I came off[1] last week on HS420 Marathons (which are apparently now the same thing as the Plus, with a narrower puncture band) at similar pressure. Road was damp and non-specifically slippery under foot from presumed leaf residue (no actual chutney, though the gutter was full of it), with a slight adverse camber. Temperature about 12C. It's a route I take several times a week, and that's the first time I've had a problem there.
That bike's been wearing those tyres since the spring of 2016, when they replaced worn-out HS368s. Though thinking about it I was off the bike last autumn with tendinitis, so this was one of their first outings in chutney season...
[1] I was fine, the bike wasn't.