Using pencilkit to write or highlight somentimes the configurations that I’m using in that moment just change by itself to previous ones. ( colors, size of pen).
Other recurrent problem is the fact of my hand, change page’s zoom when I’m writing.
Firstly it could be the “Line Detect” issue for the accidental change of your handwriting. You can disable it by clicking the “” button next to the pen and disable ‘Line Detect’.
If you don’t see the “” button, just switch to another pen (like eraser) and then switch back, then it will appear.
If this still disturbs you, you could also disable PencilKit and turn to our original annotation tools. Click ‘…’ at top-right corner and disable PencilKit.
Are you sure you’re not accidentally double tapping the apple pencil (if you have pencil v2)? This usually switches tools - mine is set to swap between the plan and the eraser but I think it can be set to swap between previous tools. I accidentally double tap mine all the time