Here's what it says over serial when Error 85 is generated:
Read Block: 000000 - Read phase 2: Host didn't respond with a 55!
Edit: Okay, this is weird. The ESProFile is still being powered by my laptop's USB port (serial communication still open) and I powered up the Lisa again and it worked, booting straight into LOS 1.2 as expected. Huh.
After further attempts while powering the ESProFile from my laptop's USB port (serial communication open or closed) and from the wall outlet USB port... sometimes it works, sometimes it doesn't - power source and serial comm status don't seem to affect the issue. After plugging in the ESProFile, the first boot into Selector and then LOS 1.2 always works fine. Subsequently powering down the Lisa, then powering it up again, results in Error 85 about 75% of the time, while 25% of the time it boots as normal.
So, it seems that the host (is that Lisa? or is that something in the ESProFile?) frequently doesn't "respond with a 55" in the expected manner or timeframe which breaks things. Note that this issue is unique to the ESProFile and I haven't encountered Error 85 with a 5MB ProFile, X/ProFile + voltage regulator in a ProFile case, or the ArcaneByte Cameo/Aphid emulator on the same machine using its built-in parallel port.