With this, we've applied +5V to two BUS pins of the adapter.
That shouldn't damage the Amiga, but on the other hand, we've grounded several lines of the D31:0 data bus, among other things.
This part of the bus goes VIA to the Paula Budgie and other places.
If any of these chips connected directly to the bus has a damaged pin and is interfering with the bus, then we have the problem.
I would check the D0:31 signals with an oscilloscope to see if any are dead.
This would be the easy part.
If a damaged line is found, then we would have to disconnect or figure out which of the connected components is faulty.
Turn it on for a while and check that nothing is overheating, that would be a good way to suspect something, since starting to desolder on the board without being sure, could cause damage and more problems.