Hi robelee,
Apparently forum member NRG has found the fundamental cause of the problem in the thread 'Pro Connect feels rough'. He has recorded the video evidence showing where the issue comes from - i.e. faulty design of the 9t motor sprocket. I was able to solve my issue immediately by switching to the 11t motor sprocket. Other than that or constantly renewing the 9t motor sprocket, I do not see much other solutions. One could try to increase chain tension as you did, but will it prevent the problem from reappearing, that is the question.
Apparently forum member NRG has found the fundamental cause of the problem in the thread 'Pro Connect feels rough'. He has recorded the video evidence showing where the issue comes from - i.e. faulty design of the 9t motor sprocket. I was able to solve my issue immediately by switching to the 11t motor sprocket. Other than that or constantly renewing the 9t motor sprocket, I do not see much other solutions. One could try to increase chain tension as you did, but will it prevent the problem from reappearing, that is the question.