I was on 3.12 (on H2O) until just a month or so ago when I decided to test some 32-bit stuff for myself, although I never quite got around to that in practice. Anyway, the only real change I'm aware of since 2014-ish in the non-Nickel part of these devices is the recent introduction of 32-bit.
This wifi stuff is simply a variable supplied by the system (see
here), so is it possible that advboot somehow sets it incorrectly?