I've had issues like this for several years, but mine can be more attributed to neuropathy from chemo.
I can say that when carrying a heavy load, say 70+ pounds, I can get numbness all the way down one leg or another. Adjusting my pack/belt helps.
The first thing I definitely do not do is weighted hiking throughout the year. Cardio, weights, and core exercises take care of that issue.
I wish I had a solution for the OP. Could be swelling/inflammation, which could be a nerve being moved out of its channel, which would cause this issue.
Maybe ice, massage, or both may help?
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