This is a well known issue here in these iPad communities.
Take a look at these ongoing, long standing, longer posts on the subject of this intermittent, unresponsive touch screen issue below.
This issue has been going on for a full year, now!
There is STILL no “official” confirmed solution/fix from Apple, to date!
None.
That is because this issue is either STILL only affecting a growing, but still very small minority of iPad Pro users OR iPad Pro users are simply NOT reporting this issue enough here in these official Apple iPad support communities OR simply NOT posting enough feedback to Apple about this intermittent, unresponsive iPad Pro touch screen issue to alert the proper responsible and cognizant Apple employees and teams and get them working on this iPad Pro touch screen problem.
Look at these ongoing post links below.
iPad Pro touch screen intermittent unresp... - Apple Community
https://discussions.apple.com/thread/250085450
iPad Pro screen unresponsive - Apple Community
https://discussions.apple.com/thread/8658399
iPad Pro 12.9” not responding to touch in... - Apple Community
https://discussions.apple.com/thread/8396370
The best you can do is continue alert Apple to this growing issue.
The only way to get Apple to, DIRECTLY, listen to you is to use their feedback portion of their website.
iPad Feedback
http://www.apple.com/feedback/ipad.html
Cognizant Apple employees read ALL feedback generated from all of the various feedback pages and transfers the data to the proper and responsible Apple teams and personnel , but NO Apple employees will ever respond with any type of direct, individual replies from the feedback you post.
You can post multiple feedback to these feedback pages.
The more users that post product feedback about any product issue, the faster Apple is made aware and starts working on a fix/solution for a future software update.
Also, you may want to phone contact Apple, directly in Cupertino, California, and calmly talk to an Apple customer service employee about this issue via the link below.
https://www.apple.com/contact/
Good Luck to You!