This problem ended my running career back in 1984 at age 24. No one could diagnose. No, pain, just loss of control especially when fatiqued. I had 3 exploratory surgeries, many visits to the chiropractor,taping, etc. with no positive (and some additional negative) results.
It started at the end of a hard repeat mile session on the track in February of that year and got progressively worse where it would hit in the last mile or so of a 5K or 10K on the track. Same issue on the roads. Trails did not help. I was extremely frustrated as I was (for me) very fit, qualified for the Trials that year on one leg - it let go at 20 laps, but I was well ahead of the OT qualifying time. Basically watched guys that were dying pass me in the last 5 laps as I dropped from the lead group to 10th and lost 25 seconds on them. I felt great, except I couldn't control my damn leg.
By the time the Trials rolled around in June it was worse. I had the same experinence in both the 5K and 10K prelims and did not make either final. The Trials were my last races ever.
After all this time, I do believe it is related to my slight scoliosis combined with many years of hard running altering the nerve signals to my left leg. I've never been able to fix it.
I would hope that today's technology would come up with a non-invasive way to address this. Interesting as I thought I was the only one who ever had this problem.