Then you notice polygon isolation (clearance between polygon and trace) is too large. Pins that used to be connected to the polygon aren't. You can't manually reduce isolation. How do I fix this strange behavior?
|DRC errors? I swear this was working yesterday!
The clearance value in the Edit > Net Classes dialog was set to 0.355mm (~13 mil) for some reason. Zeroing it fixed the DRC errors and isolation issues.
The Net Classes clearance value overrides your DRU (Design Rule) file settings. OSHPark's clearance is 6 or 8 mil and I rely heavily on these tolerances in my designs. So you can see how suddenly increasing to 13 mil would blow my design.