Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce GTX 1060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 430.86
Broken: version: 2.80 (sub 74), branch: master, commit date: 2019-06-28 19:44, hash: rB5762137f3522
Short description of error
When using the Swirl Effect for a grease pencil object, GP object disappears at default setting radius =100px and Angle =90 no matter if using empty or another object in the Object field.
The only setting that shows the GP object at all and unaltered is when Radius = 0. Doesn't matter what setting is for Angle, nothing happens.
Exact steps for others to reproduce the error
Go to Object Mode and add Grease Pencil/Monkey.
Add Empty: Plain Axes or any type
Select GP Monkey and Select Effects button
Choose Swirl Effect in Add Effects drop down
Object field: choose Empty
The GP Monkey disappears, change radius to 0 and GP Monkey reappears but no swirl.