Sorry to see that. I have one of those sitting in the garage waiting for it’s maiden flight.
The FPV horizon seemed to be moving appropriately so that says the FC still “knew” where it was, even if it couldn’t or wouldn’t do anything about it.
I’m assuming you commanded the switch to FBWA? It didn’t just happen on it’s own? Did you try changing modes again to recover?
Unless you’ve cranked up your maximum angles then FBWA should have at least reduced the bank angle to max from the knife edge you were on. This would maybe rule out a radio issue.
Maybe start by looking at the servo outputs in the log. See if the aileron servo was trying to make the correction to roll to level. If the proper output was there, that could point to a servo or mechanical issue. If the output isn’t there or the output is holding the bank then it’s back to the FC.
Can’t say too much more without a log.