PDF Inking's INK sometimes depletes in Edge canary

It's true, literally, when I draw on PDF, after some time, the INK depletes. yes I'm talking about the virtual Ink.

so few minutes ago I was just pointlessly drawing on a piece of PDF and I noticed the Ink is no more drawing. when I click nothing happens. changing colors or thickness doesn't help.

i closed the PDF then opened another, same result after drawing on it for a while.

• Is there really a limitation for the virtual Ink on Edge PDF reader?
• Why?

Version 81.0.410.0 (Official build) canary (64-bit)