BMW x1 e84 strange issue, EGR? Transmission?

[Rash93]

Hi, I own a BMW X1 E84 2.0 diesel xDrive with an automatic transmission.
I’ve started experiencing a strange issue and I’m not sure what to do. I would really appreciate some help.
After driving for about 4–5 minutes, if I maintain a constant throttle between 40–80 km/h, the RPM needle starts surging (fluctuating up and down) and the car starts shuddering/jerking. As soon as I accelerate, the car runs perfectly. It also idles fine and performs well at higher speeds.
There are no error codes showing up on the diagnostics.
Thanks for the help