Have you been exercising throughout this period?

Are these all first morning voids or samples throughout the day?

The only logical explanation I can come up with is exercising habits and hydration levels. It's very possible to be down to 25-50 ng/ml one day, then go out and exercise and all of the sudden you can spike up dramatically to failure levels. Exercising is great, but burning it out of your fat, means it has to go somewhere, and that somewhere is right into your test cup.

But even so, going from 68 all the way to 351 is very extreme. Given how long you've been clean, I'm actually very shocked to hear a 351. That's very high.

Wish I had more information for you, I'm pretty stumped by this one though.