Hello there ashn1,
First, check in another app to see if the line also breaks when drawing, writing, or highlighting in landscape mode. This allows us to isolate the issue further.
Next, restart your iPad to see if that resolves the issue.
Also, be sure that your Apple Pencil is fully charged: Charge your Apple Pencil and check the battery
What iPadOS version do you currently have installed? If there are updates available, be sure to create a backup and install them as well:
1. How to back up your iPhone, iPad, and iPod touch
2. Update your iPhone, iPad, or iPod touch
In the meantime, does your palm touch the screen while writing on it in Landscape mode vs Portrait mode? We want to see if that may be a possible cause as well.
Certainly keep us posted, we’re here for you every step of the way!
Take care.