There is buffer of approx ~10922 draw calls of ANY active DrawLine's on screen.
This limitation is hidden, not explicit by minimum
By maximum, move buffer from global, to local by CanvasWidget, so every canvas has it own buffer.

This hidden buffer overflow is leading to many undefined behavior.
Glitching shadows
Glitching UI
Many more

Create simple for loop for 12000 iteration, with drawing any stroke to the canvas widget

Move buffer from global, to local by CanvasWidget, so every canvas has it own explicit buffer.