Is URB working on IOS12?
Are you sure your Apple pencil is working all the time? Mine doesn't. I had to turn mine in and get another only to have the same problem. Try and draw with your finger when the Apple pencil is not working and see if you can draw at all. If you can, it's the pencil acting up.
Vickie Villavicencio commented
Sometimes I cannot write on certain pdfs in Unreal book, but can write on most sheets...all imported same way. Very random. Use IOS12.13.6 Sierra
I regularly use the Apple Pencil
It runs on iOS12.
Would love to know if I can download and install iOS 12.1.3 on my ipad pro 12 and not have any problems with Unreal book. Love and rely on Unreal book!!!