Some exciting news! I think I found the source of the problem and the solution. I don’t want egg on my face, so I will say it again, I **think** I've found the source of the problem. I will need your help to confirm it.
First, make sure you are having the same touch issue commonly described here on a iPad Pro 2nd Gen 12.9. Specifically, you touch something actionable on the screen and nothing happens. You’ll often get an auditory feedback when you type, but nothing shows up on the screen. Eventually you’ll get a response after several tries, but sometimes you will have to reorient the screen, touch another location on the screen or kill the app. If you’re having the same symptoms, then this might work for you.
The solution is very simple, but I don’t know if many of you can live with it. Are you ready......drum roll.....
DELETE THE YOUTUBE APP!!!
That’s it. Will the problem go away 100%? Not really, but at least 95%. I occasionally get a key press drop, but not nearly as often as before. The performance is also much zippier. I was wondering if the iPad Pro was overhyped and even considered downgrading. Now, however, I am seeing significant speed improvements over my old iPad 4.
Try this solution and report back. You may also want to restart your iPad for good measure just to clear out all the evil YouTube bits and bytes that may be still lurking in the system. This might explain why some people don’t have this problem while others do. You’ll have to watch YouTube from the browser, which really *****.