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Tuning Concerns for the C43: Engine Timing

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Good day to everyone - I'm new around here, so if you could possibly be patient with me?

I have recently purchased a 2017 C43 estate, and given the success I had mapping my previous C220d, I wanted to try the same thing with my new car. To begin, I got a stage 1 remap from Celtic tuning, and I have to say that, in terms of performance, I was quite happy indeed with both the throttle responsiveness and the overall performance increases.

After playing it for a few weeks and getting accustomed to it, I began playing it more quickly and in manual mode, and that's when I spotted a huge problem... so here we go!

as I was in Sport+ and using the manual transmission, I would give it a vigorous acceleration through the gears, and the car would take off. However, as I would get into 5th gear at roughly 4100 rpm and 94 miles per hour, the engine would lose power and not go much further than that. If you shift into sixth gear, it will continue to behave the same way, i.e. it will stay at roughly 3600 rpm and will not increase any more. In the beginning, it would only do it when set to manual or Sport+ mode, but as time went on, it began doing it even when it was set to automatic, although to a lesser extent. Then, just very lately, it began to do it in the Sport and manual modes, but not in the automatic mode. There was no impact on any of the other engine modes, either manual or automatic.

In an effort to find a solution to this problem, I contacted Celtic, and together we attempted the following:
Remove the map from its case and reload it into the vehicle.
Nothing changed despite using it in a variety of weather situations and at various stages of driving, such as after a short run, a medium run, a long run, and so on.
Tested the configurations using the individual mode.

Nothing I tried worked, and the problem persisted even after I removed the map, so I decided to test whether the vehicle itself would be the cause of the problem. However, the car is operating normally in all of its modes and settings.

Celtic said that it is a frequently used map, but they have never had any problems with it. Since I purchased the super unleaded gasoline in September of last year, I have used it exclusively ever since, so that explanation is out of the question.

Has anybody come across this before, or has any idea what it may be?

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It's possible that the automobile is overboosting, which would cause the engine control unit to reduce the boost pressure.
Do you have anything (like Carly or another diagnostic) that can measure how many pounds per square inch (psi) of force the turbo is exerting? If you are located anywhere around Essex, you are welcome to use mine.

Personally, I would remove the map and do either GAD or MSL adjustment.

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After you brought it up and after I did some research, it seems that it might be the one responsible for the problem. I had the map removed the week before last, and I've been in touch with MSL to try to schedule an appointment for it so that they can potentially map it correctly for me.

I am grateful for your response.

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