Mmmm, if it has new(ish) plugs, leads and coils. I'd lean towards crank sensor dying maybe. They tend to get worse with temperature but thats not always the case, just common, I even had one that did the opposite - really had and spluttery when first started and cleared up.
These often don't report a fault in the ecu and if they do they just report a misfire rather than the sensor itself - i think if it completely failed and went open circuit it might flag up but i have never seen that happen on a FIRE engine.
Cheap as chips from S4P atm...
https://www.shop4parts.co.uk/?name=store&op=Details&ProdID=828&sku=72819
Bizarrely for me its not my cables, I can try plugging it in and it just didn't connecct with IAW Scan, but i could close that and open
MES without touching the cables and it always worked - no idea why, perhaps it was just an issue with my particular ecu. I don't have it anymore so who knows, i just used
MES on the 16v and it just worked so never really bothered trying to get IAW Scan the work properly.