Anyway. Here's the evidence. Under the second hole is a broken tap.
There are guys who claim they have never broken a tap. I'm not one of them.
You could just add another screw by drilling right through the bracket. But looking at the assembly, I'm not sure it's needed. That's prolly why you left it. You could hide the evidence by drilling some more holes in the bracket so it looks like you just chose one of them.... LOL!
I'd use a course thread too - even if the kit came with fine.
Two other tricks I use to tap cast iron are frequent cleanout and small increments - especially in a horizontal hole. Another is an oversize hole with 50-60% thread.