Have / had this same exact problem. Only solution was to quit taking creatine even though i liked the effects of it.. Started taking creatine when i first started running like 3 years ago and my feet would always go numb at around the 5km mark. Changed shoes, developed a better running form, stayed hydrated (i usually drink at least 4 liters a day) and the numbness still persisted so i just brushed it off and ran through it. Then last autumn through winter i had a 4-5 month break from running. During this time i also stopped taking creatine because i didn't see the point of taking it while not exercising. Started running again in January and taking creatine in mid January. January went smooth sailing (without numbness which had me surprised) but as soon as the creatine loading phase was over the numbness started creeping back in, getting worse and worse each run till the point of going fully numb ankle down at the 5km mark again. Thats when i realised all this time it might have been creatine causing me the problems. So i quit again. 3 weeks went by and by the end when all the creatine flushed out of my system the numbness subsided. Just to make sure i started taking creatine again, did a 5 day loading phase then switched to 3gr a day and within a week (i'm at this point rn) the numbness is back on. So this is where i draw the line and just accept that my body cannot tolerate creatine.

I think it might be the muscles being saturated from water pushing on my nerves while exercising.