Minimum compression for a non-SP 916 is 113psi (Haynes spec). Motor may be a bit tired, but compression is not the issue. Cam marks are all lined up as they should be when crank pulley dot aligns with case mark, so I'm ruling that out too. Temp or other sensor issue sounds most feasible. Hopefully get time to sort this week- we're in another lockdown and kids are off school so tinkering in the shed is at a bare minimum.