Hi Paul! Thank you for responding!
This logo consists of 4 different parts including the one with letters. I didn’t apply Grease Pencil’s Line Art Modifiers to the whole scene, because I want to animate those 4 parts differently later.
I added the Line Art modifiers the way you suggested.
But I noticed that then, in the process, I copied the asset just in case, before adding modifiers. And I also had a camera copied that I found on the hidden layer. Could this have caused the issue to appear? And if so, how do you make one of them active if you have two or more cameras?
By the way I bought your Blender Core Skills the Ultimate Blender Basics Bundle from Humble Bundle, and it helps me a lot to learn Blender better!