Assuming you are doing factory resets here, as I am sure you are, there are really only 2 options here - the resets are not working for some reason or there is some hardware variation that does not like the new firmware. For most this firmware is very stable and very reliable.
It is weird that 3 people now seem to have trouble straight after reset, but many months back I too had very strange results with firmware that was otherwise considered good. I thought this was all in the past, but maybe I've just been lucky. This router does seem to sometimes get itself in a mess that can be hard to reset from, regardless of firmware version.
Thanks Jong. Not that it should matter but I picked up a newegg refurbished. Wonder if there is some hardware variation like you mentioned.