Oh, though the system is behaving in a different way now, it seems.
At least on my machine (chipset HM470, ME 14), the HAP bit is set in the flash descriptor area. When looking at the stock and the modded flash descriptors side by side, these are the changes:
The first four squares represent the access level for each regions (BIOS, ME, GbE and EC), which I modded to “FF” to allow read/write access to all of them (as described here).
Then, the fifth square is the HAP bit.
It seems the format of the flash descriptor varies depending on ME version. From ME 11 onwards, it’s like mine. Older versions are different. But you say you’re using ME 13.5, so it should be like mine.
Perhaps you can check and compare with a backup?