When temps start to drop, any small problems will start to show.
3 things only are needed for a direct injected diesel to fire
If timing is out at cranking, it could not allow enough air into combustion chamber, could also be valve problems if they are not opening enough but still in time.
Air filter could be blocked or water logged.
For fuel to be fired it needs to have no air bubbles in the lines and pump, to allow high enough fuel pressure to build up at the slow cranking speed.
The pump has to be turning quick enough to create the required fuel pressure at cranking, which could be restricted due to voltage, tight starter, tight engine due to oil thickness, either wrong or old engine oil.
The fuel pump requires a minimum cranking voltage to operate also otherwise it will never fire. Again could be battery, connections, starter pulling too much for whatever reason.
The fuel also needs to atomise fully to ignite, it may not atomise if injectors are worn, or low pressure due to restrictions in low pressure side like the fuel filter, or air.
Or just worn pump.
The heat from a direct injected diesel engine is produced only by compression of air in the cylinders.
This can only be done if the right amount of air is compressed and quick enough.
If you turn the engine by hand you will not raise the compression/heat anywhere near enough for ignition.
If an engine is turned too slowly the air is not compressed quick enough to create enough heat, it may be quick enough to still fire the fuel so you would get unburnt diesel smoke from exhaust.
If an engine has a cylinder or 2 with lower compression then if it were low enough to stop the ignition, you would get a miss fire when started.
also if glow plugs were needed to give extra heat then again you would get a misfire once started At the cylinder with faulty glow plug.
If an engines compression was dropped from 20 to 12 bar if it had fuel firing still and enough air the compressed air at that level is still enough to create enough heat even in minus conditions.
If the engines compression dropped further it would would be uneven wear or damage so again you would get a misfire when eventually fired.
Engine oil thickens, you could also have the incorrect oil in so will be far to thick, restricting cranking speed.
A low charged battery will drop even further in the cold also further reducing engine cranking speed.
You can not tell a cranking speed by just listening to the engine turning, or the actual cranking voltage.
the cranking voltage will need to be high enough to actually energise the fuel pump
So cranking speed, and voltage are needed to create enough heat from compression and fuel to injected and atomised.