You fucked yourself. I am the guy that begged people to never run a bitmaintech firmware.
many reason and stories abound.
basically you are bricked.
first is that a batch 5,6,7,8
bitmaintech did 11 batches so far and 1,2,3 will plave with each other as long as you di not upgrade firmware.
if you are and older batch like a six look for a batch six controller in the market place.
so you need to know your batch number and then ask around for help.
the 1,2,3 and the 9,10,11 are two sets then middle batches vary. any they started striping the controllers down so you really need to know what one you have.
I have a batch 2 the controller allows be to attach a second s-7's set of boards but only from the 1,2,3 batches.
I pushed not to do it on any that did not run off SD cards. S4's and C1's ran off sd card.... bad flash reflash the sd card simple and nice. But cheapness made ones run without sd cards. Removes your ability to fix a brick quickly. Ever since I bricked a S3 I have mentioned many times I don't update unless big flaw. Only one that met this was some S3 reset did not work.... so big flaw need to update. Been a LONG time since a good reason.
On S7 if works... don't touch firmware. The hard part OP is you need to try to go back to working firmware or do another flash... to see if it is a bad flash. But problem is your power off's. If you get a single power off during your re-flashing you have a brick. So your in a hard spot. Might look at re-ordering a BBB board for your batch if truly is F'ed and count it as lesson learned.