Hello ayvi_,
We'd recommend cleaning the iPad and Apple Pencil using these steps: How to clean your Apple products
iPad
Handle your iPad with care to maintain its appearance. If you're concerned about scratching or abrasion, you can use one of the many cases sold separately. To clean iPad, unplug all cables and turn off iPad (press and hold the Sleep/Wake button, and then slide the onscreen slider). Use a soft, slightly damp, lint-free cloth. Avoid getting moisture in openings. Don't use window cleaners, household cleaners, compressed air, aerosol sprays, solvents, ammonia, abrasives, or cleaners containing hydrogen peroxide to clean iPad. iPad has an oleophobic coating on the screen; simply wipe iPad's screen with a soft, lint-free cloth to remove oil left by your hands. The ability of this coating to repel oil will diminish over time with normal usage, and rubbing the screen with an abrasive material will further diminish its effect and might scratch your screen.
Apple Pencil
To clean your Apple Pencil, use a soft, slightly damp, lint-free cloth. With the damp cloth, wipe your Apple Pencil from the tip end—but not the tip itself—toward the other end of your Apple Pencil. Don’t allow moisture to get inside the seam between the tip and the body of your Apple Pencil.
If you haven't yet, make sure you've tested a simple restart of the iPad: Restart your iPad
After these steps, test the issue to see if you can reproduce it or not. When you use apps or Markup with the Apple Pencil, make sure you're selecting on different options for drawing. For example, you could try using the Highlighter or Pencil options instead of the Marker: Draw in apps with Markup on iPad
Should it persist, please reply back to let us know. Include the current iPadOS version in your reply.
Wishing you well, take care.