Sounds like the Pyrodex got contaminated with moisture. Maybe last time at the range? Did you take the whole jug to the range? Where do you keep your powders? The Goexhas re-drying capabilities. I always use FFF/P with my sidelocks to help avoid stuff like this.The finer granules are easier toflow thru the powder channels - then under the nipple.

I would try to resolve the remaining RS powder hang-fire by laying out some plain white sheets of computer paper on a flat surface & spreading out the powder for a day or-so in a dry environment to remove any moisture it might have. Don't use anypaper with ink & pinch loose any clumps found in the jug of powder.

Then try it again at the range. If the weather is not favorable, only take the amount of powder you need. When you return home, don't put the range powder back in the original jug. Use it for range work only.

When all else fails... change the nipple & powder. It's possible the nipple is at fault here & only ignites the Goex instantly because Goex ignites easier than Pyrodex.