Interesting. I use my mini 6 in the case 99% of the time. I didn’t test without the case. One thing to keep in mind is people have varying electrical characteristics. I had an uncle who couldn’t wear mechanical watches because they would always die on his wrist; an extreme case.I'm 99% certain I got it figured out. It's a grounding/static electricity issue. Whenever (without the case) I touch the ipad metal chasis on the side with one finger while writing, it NEVER skips with my palm on the screen (even with the lightest touch of writing). But when I take my finger off it skips. Put my finger back on, it stops skipping. This is absolutely pathetic for a $600 device. So I pretty much have to use this thing without a case and to touch the side with my finger to prevent any skipping.
And my case is the Apple Smart Folio which leaves the edges of the iPad exposed.