2019 DF115A, 20 hrs with very rough idle

[Chazley8871]

Before the 10 to 12 hour mark during break-in the rough idle began almost unnoticeable at first, but has slowly gotten worse over time. The effect is made worse when in gear, either forward or reverse, the gear train makes an audible backlash sound like the engine is accelerating and decelerating quickly between each revolution. Every other aspect of engine performance is fantastic. I just got it back from the 20 hour service and it made no difference. The establishment I went to is backed up for repairs and troubleshooting so they would have to book me at least a month out to have a look at it. It concerns me that without knowing what is causing the issue, it might be doing harm to the engine. Opinions or suggestions would be appreciated.

edit : I should add that the rough idle doesn't really get bad until the engine runs for about 3 to 5 minutes.