I got a second opinion from another garage, and they said that the issue doesn't resemble diesel injector problems. They performed the same tests as the first garage, and the return fuel from the injector chart looked average.
They believe the crankcase sensor had failed. After installing a new one, the car started running smoothly.
However, my injection system still needs attention as soon as possible.
If anyone had the same issue, look at the crankcase sensor location, passenger side (UK), front wheel arch plastic needs to be removed. It's there.