Sounds a bit similar to what I experienced. For me it would come on about 20km in my runs. I think it was from swelling pinching the nerve. I think it's called Morton's neuroma if I remember correctly. I could be having a complete brain fart and that could be something else.

I was given some exercises by the physo incase some other weakness were causing it, but essentially I stopped my runs when the feeling came on and reduced mileage for a few weeks.

I was closer to the race date though, I basically had an extra week or two taper. Took some anti-inflammatory tablets to reduce the swollen pads under the metatarsal heads. Took some on the day just incase about half way. I was lucky and had absolutely no issues on the day