There are problems with starting the engine of a BMW 320d e90 from 2006, specifically related to the cranking process.

[WolfieBase]

Greetings, gentlemen.

I own a BMW 320d e90 2006 model and around 7 months ago, I began encountering difficulties with starting the engine.

Initially, I believed that the winter season and the occurrence of glow plug faults on the OBD2 system were related, therefore I decided to do the following action:

    Four glow plugs and a glow plug relay.

In addition, I replaced the battery with a Monbat AGM 100ah, since the prior one was a non-AGM battery of poor quality.

The problem had previously been resolved, but it has again reappeared. I suspected that the Starter would be the cause this time, so I thoroughly fixed it. However, this did not resolve the issue.

I also consulted a professional who verified that there are no problems with the key, and I am not seeing any key errors on the dashboard.

I am entering the key and activating the START/STOP button to initiate the functioning of all systems (without starting the engine yet).
After a brief 10-second delay, I engage the clutch pedal and activate the START/STOP button.

    When the temperature is about 7-10 degrees Celsius, the engine exhibits a beginning behaviour where it cranks for around 1-3 seconds before abruptly halting, indicating a loss of power.
    In addition, when the temperature is rather chilly, rather than briefly engaging the crank and experiencing a loss of power, the engine may sustain cranking for an extended duration, and I deliberately intervene to stop it.
    If the temperature outdoors exceeds 20 degrees Celsius, the device will begin without encountering any problems, based on current observations.
    If I omit the first push of the START/STOP button to initiate all systems and promptly engage the clutch to start the engine, there are three possible outcomes: the engine may crank for a little period and then lose power, it may continue cranking until it stops, or it may start without any apparent difficulty. Irrespective of the weather conditions or temperature, there are no regulations in place.

(Additional information that may be helpful) Approximately two months ago, I brought my vehicle to the automotive repair shop for routine maintenance, including an oil change and filter replacement. During this visit, the mechanic informed me that there is a problem with the engine.
The engine problem lies in the Piston Rings, which need replacement. As a result, there is excessive pressure in the carter, and the engine is using more oil than anticipated.
Prior to receiving this information, the occurrence of the engine starting problem was limited to a single instance.
I am uncertain about the whole accuracy of this information, since I want to verify it with a more dependable specialist. However, if it is really accurate, I shall proceed with the task of reconstructing the engine.

Perhaps these two things are intricately linked?
If not, what may be a potential problem?

[DMGRS]

whether the engine has worn piston rings, it might lead to difficulties in starting. However, how can he determine whether the piston rings are really worn? Was a compression test performed on it?

[WolfieBase]

According to what I was informed, he conducted a compression test and found that the level of compression is higher than anticipated.
However, if that is the problem, shouldn't starting the engine be problematic regardless of whether it is warm or somewhat cold?

[DreamCatcher88]

Does the vehicle emit a dense plume of white smoke from the exhaust, accompanied by a distinct diesel odour, after a cold start?
If the answer is yes, it might be a potential sign of poor compression.

It seems quite dubious that the problem arose subsequent after the service.....?

[DMGRS]

Warm engines have variations in tolerances, which may impact compression. However, you said that there is an excessive amount of compression. Is that correct?
You need to get the figures from him in order to determine if they are low, high, or within the typical range.

[DreamCatcher88]

I have never encountered the concept of excessive compression. Presumably, the presence of fluid in the combustion chamber may be attributed to substances such as gasoline, oil, or coolant.

[alabbasi]

As mentioned by DreamCatcher88 above, this is also a novel concept to me.