Apple Pencil highlighter tool draws thin line when marking from the right side

This is exactly the problem I’m having. The highlighter draws a thin horizontal line and a thick vertical line. It happened all of a sudden while I was highlighting a PDF document in Files on my iPad. I tried restarting, changed the nib, unpaired/re-paired the Pencil, updated to iOS 17.2 with no improvement. It literally changed while I was highlighting a line of text. Very frustrating since I used the Apple Pencil for marking up documents I read for school. The pen, colored pencil, crayon, etc. are not doing this. It’s just the highlighter. I have been using the Pencil for months with no issues. Cannot find a setting to tweak.

I'm unable to replicate your issue.

Try a forced-restart of your iPad - as this may clear an isolated software issue:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

If the problem persists after performing the restart, it may be necessary to reset your iPad settings. While this reset will not cause any loss of data, as a precaution, it is always wise to ensure that you have a current iCloud or iTunes backup before performing the reset:

How to back up your iPhone, iPad, and iPod touch - Apple Support

When you are happy to proceed, you can perform the reset from iPad settings:

Settings > General > Transfer or Reset iPad > Reset > Reset All Settings

If the problem still doesn’t clear, the next step is to reset the iPad to factory settings:

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

Otherwise, you would be best advised to seek assistance directly from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page.

Alternatively and perhaps easier, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:

https://apps.apple.com/app/apple-support/id1130498044

I have been having the same issue. Tried restarting, changed the nib, updated to iOS 17.2, did a hard restart, all with no success. What finally worked is turning on the rotation lock, but that only worked one time. The issue came right back. I’ve been using the highlighter for months with no issues, but two days ago the highlighter started making a thin horizontal line instead of a thick horizontal line while I was in the middle of highlighting a line of text in a PDF in Files on iPad Pro. I highlight left to right using the built in Apple markup tools. Not being able to highlight text makes the Apple Pencil close to useless for me.

Your photo suggests that you are using a third-party drawing App. The illustrated drawing tools do not correspond to those of an Apple App...

As you are seemingly using a third-party App, you will need to seek assistance from the relevant Developer:

How to contact an app developer - Apple Support

were you able to solve the issue? my iPad has been doing it the last couple days and I dont know how to fix it

Remember that your Apple Pencil senses its vertical angle (tilt) to the screen.

When using the highlighter drawing tool perpendicular to the screen (i.e., 90°), the highlighter will draw a narrow line. By contrast, using the Pencil near horizontal to the screen, you will see a very broad highlight. As such, by varying the angle from vertical, you are able to control the width of the highlight.

For some Apps, the Pencil is also sensitive to pressure. A lighter touch of the Pencil to the screen produces the lightest line; more pressure produces a darker line.

This description may help with understanding how Apple Pencil is used to draw:

https://www.macrumors.com/guide/apple-pencil/