Fluid Brush Layer lag Animate CC 20.5.1

Hello ,

Version of Adobe Animate CC : 20.5.1 When I draw on layers that have several keyframes I notice that the Fluid Brush tool starts to lag behind. However, on a blank layer the strokes are very responsive. Any idea what maybe causing this?

Here are my PC specs:  

Here is a video of my issue:

Thanks for all of the hard work, hope to hear back from you.