Heal selection

[Ofnuts]

Digging the source code:

Code:

/*
  Rare user error: all corpus pixels transparent or not selected (mask empty.) Which means we can't synthesize.
  This error NOT occur in GIMP if selection does not intersect, since then we use the whole drawable.
  */

So, unless there is a bug, there is no selection, despite all evidence to the contrary. But we are in 2.10, did you to anything to "commit" the selection before calling the plugin (double-click, or [Enter])?