problem occurs only when engine is cold. takes up to 10 min, then it suddenly starts if nothing is wrong. I know there is a huge battery drain of 0.6A when car is in sleeping mode. It is definitly a low voltage problem, but I can not explain, why engine re-starts without problems as soon as it has run abt 2 minutes. This time is for sure not enough to charge the battery to a level which could be considered fully charged....
Battery is also brand new and up to specs ( CCA 920 A / 110 Ah). So definitely not a battery issue either

I have the exact same issue in my 2005 vogue with 4.4 jaguar. I have purchased the RR from a Japanese auction a month ago and it had been doing the same thing ever since. The battery is a bosch silver x slx 1b which is a 900 cc 110AH huge battery that to with December 2020 install date on it. I tried to charge the battery with a 7 stage charger and it went to the 6 stage in a couple of minutes and completed charging in less than 30 minutes. So the battery is new as. When it doesn't start, I hold the key twisted clockwise and it does those clicks 6 to 10 times with 10 seconds gap and the RR starts like nothing happened. On 2 occasions, the above method didn't work. One time I just jump started it with another car and it was fine. The second time I came back after an hour and it started on the 1st attempt. Also when it doesn't start, I notice the dimming of the interior lights and the windows go up and down at snail's pace. Also when I crank it, it doesn't just clicks, it actually cranks for half a second or lets say one stroke of the pistons. It also flashes the HID headlights for that half a second even when the switch is at Off position.

we are very close to find the cause. keep you posted

I have read a discussion elsewhere that the cause is the solenoid connectors in the Denso starter motor. Even if one changes the motor, the issues returns after a few years and it was advised to rebuild the motor with heavy duty solenoids.
To verify it, we can tap the motor with a hammer when someone else is turning the key. I will try it next time and let you know.

finally found the problem it was the transmission relais, a problem which occured with BMW X5 4.4 often as well. Hope it fixes yours as well

Michael15 said:

finally found the problem it was the transmission relais, a problem which occured with BMW X5 4.4 often as well. Hope it fixes yours as well

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I have the jag 4.4 with 6 speed trans. Do you reckon it would be the same. People with later L322s ( push start ones) also have the same problem