Everyone in this post needs to inform Apple about this.
This is a known, growing issue across all iPad Pro year and models ( even the brand new 2018, 3rd gen iPad Pro models ) and it is starting to affect both the 2018 and 2017 6th and 5th gen 9.7 inch screen iPads, too!!
I am more than convinced, now than ever, that this growing issue is NOT hardware related, but either iOS 11 and/or iOS 12 related bug.
I have a 1st gen, 12.9 inch screen iPad Pro still running iOS 10.3.3 and I am NOT experiencing these recent intermittent touch screen issues.
Some Posters/Users have stated here that this unresponsive touch issue started sometime late in the iOS 11 update cycle, but seems more pervasive in iOS 12, now!
There is, at least, one of these “iPad Pro unresponsive touch screen issues” posts a day!
Currently there is no fix yet from Apple.
The best everyone here can do is 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.
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.
Contact - How to Contact Us - Apple
Best of Luck to All of You!