Hi I have the same kind of problem :
Running on Mac OS X 10.12.5 last logic X version, using USB only for audio / MIDI (aggregate axefX + fireface800)
last axefx driver version. my usb cable is fine
Priori to V8, I had 0 problems with axe edit, never experimented a time out.
Now, The axeFx is seen as connected in axeFX when I power it
but I always get a timeout after some seconds or minutes.
If I don't run logic (of course, I get no sound), it works after more than 1 hour : I can switch between pages and move the pots.
I've tried to go to midi 15 and no differences.
No changes made in logic or OS. As soon as I launch logic -> time out after some seconds
It seems for me a consequence of the upgrade to V8 and /or last axe edit version
My midi cable is a good one and not faulty.
So, for now, I can't really use my axefx. Too sad