I had the same issue with the same board - but udated from 6.13.
It's worth a shot to try the reset solder pad on the board itself (left to the NAND, below the miniPCI slot.
In my case this didn't work either so I returned it for RMA.
But it's only one out of ten 912 which behaved like this.
I updated more than 70 other devices (mipsbe, tile, ppc) to 6.17 without any issue.
MTCNA, MTCUME, MTCWE
There are 10 types of people: Those who understand binary and those who don't.
There are two types of people: Those who can extrapolate from incomplete data