Incremental Refresh - M query folding.

Hi, I'm trying to apply incremental refresh to one of the tables in my model, but I get a warning that "Unable to confirm the M query can be folded. I did not get this warninig when I initally applied incremental refresh to this dataset. I had this issue where the incremental refreh would get deactivated automatically, and after I tried to reapply  incremental refresh, I got a similar error. A refresh of all the tables in the power query editor seemed to fix this issue and I was able to apply incremental refreh without the warning and everything was back to normal. This time however, even after refreshing all the tables in the power query editor, I still get this warning message and incremental refresh takes longer than a normal refresh. 

In the power query editor, I verified if the applied steps can be folded, I found that only for the first step M query cannot be folded. But this is the source step and not under my control. Is there any way to overcome this issue and apply incremental refresh ??