Got the same problem on 1 S9 from batch 21-30 november, with APW3+ PSU.

bminer not found....

I tried different firmwares:
- fixed frequency 550MHz
- autofreq from August 15

I did several soft and hard reboots of the miner. It finally worked but I really don't know why.

That seems totally random.

If Bitmain could explain what's going on that'd be great