In Illustrator 2019, freeform gradients were unable to render in complex compound paths. I was attempting to add a freeform gradient within a compound path/grouped object set of leaves (about 20) of various shapes and sizes. I had used compond paths to add a freeform gradient to two objects previously (although with a few bugs - see bug titled "Illustrator 2019 Freeform Gradient and compund paths not quite right" in Other...), expecting the gradient to render. Although it sounded as though my computer was working hard to process the effect, nothing rendered after 5 minutes and so I gave up, resorting to a clipping mask solution instead.

DELL running Windows 10
Processor: Intel(R) Core (TM) 17-6600U CPU @2.60GHz 2.80 GHz
RAM: 16.0 GB (15.7 usable)