Always flawless firing .40 P229 GOTM is suddenly failing to feed - Like flipping a light switch it is failing to feed.
Same White Box Winchester, or Federal ammo I've always used. Same multiple mags.
After 1st occurrence I ordered new Wolf magazine springs and Sig blue 17lb recoil spring.

It is still failing to feed. No, I didn't go limp wrist-ed.
Any help would be appreciated.
In case I need one, does anyone know a Good Sig gunsmith close to Chicago-land?
Could I send it into Sig for evaluation and/or repair?

I would try a complete new mag usually a FTF on any of my sigs is mag spring or mag..
Also ensure the mag release button is not worn.
You could also polish the feed ramp with Flitz

+1 on polishing the feed ramp. My old reliable 229 in 40 started nose diving on the ramp. I sent it back to Sig and all they did was polish the ramp to a mirror white metal. Their feed ramps are blued and that bluing can't be polished as smooth as the bare steel. I now polish the feed ramp on all my new guns. I use a small cone shaped pad on my Dremel and put the Flitz to it until it shines.

My approach would be to first thoroughly clean and lube the gun, disassemble and clean the mags. Next step would be to change out the mag and recoil springs. Jmo...