In the past few days, we heard a lot of reports that the palm rejection of the Apple Pencil is not working properly, letters are randomly disappearing and pages are moving when placing the hand on the screen.
This is a bug with the Apple Pencil in the latest beta version of iOS 12.3 that Apple at the end of March.
Here are a few forum threads that discuss this problem:
If you haven't updated, please do not update to iOS 12.3 beta before Apple hasn't fixed this bug.
If you have already updated we recommend downgrading to the official iOS version. Here is how: https://support.apple.com/en-us/HT203282