Boyes

Has the car been remapped at all? Most remaps swap from MAF to map for the smoke calculation so it would serve no real benefit investigating apart from monitoring air into the motor through vcds. Just a thought.

Usually that would be fine for torsion value, have a read of darkside's little guide for PD's. https://www.darksidedevelopments.co.uk/Blog/pd-engine-hardware-tweaks/ Have you logged the coolant temperature sensor, between that or the thermostat it will either run cold, or think it's running colder that it is? The only other thing I could suggest is injector fouling. I would be looking for blocking turbo veins or checking the injector deviation?

Have you checked the torson value is close to 0/0.5? Some garage don't check this after a cambelt change?

I had a similar issue, but all cars are different; when it's really cold I prime the fuel line at least twice with the key, this also gives it another glow plug cycle, if I don't do this it cranks for 10-15 seconds before chugging to life. The other thing I did which helped, although you stated crank speed was good was new starter/brushes, my crank speed seemed to be slowing so took longer to start till it give up (this took months) I fitted new brushes and it's been golden and spins over so much quicker, which helps starting immensely.

Briskoda - Fabia Mk1 Light Switch back light repair This might help

Have you checked for an increase in rolling resistance, dragging hand brake etc? Something outside the engine, just a thought.

Have you checked the idlers? No damage to the edge of the belt (rubbing on the engine) I know it's difficult to isolate the noise, had something similar on mine and turned out the be a noisey idler bearing (like a squeaky alternator tensioner) sprayed some WD-40 on trying to identify the noise (on the bearing, not the belt) and the noise went away and hasn't reappeared it previously use to make the noise in the mornings, and go away once warmed up more so on colder mornings.