The bugs actually bit you? Mayflies caddis stoneflies midges etc don't bite. It sounds maybe like they were blackflies?
It sounds like you were definitely getting hits, as opposed to last minute refusals but not sure what the problem was. Sometimes too much slack line makes it difficult to set the hook. Sometimes you can break a point off banging flies off rocks while casting, but you would have noticed when you changed flies.
I have a tendency to strike too soon pulling the fly out of a fishes mouth, but that can't be it--- at least not with that hit you got on the brassie while nymphing. An indicator moving upstream is a pretty good sign it's a fish
Sometimes there are just days like that and all you can do is shake your head.
Hopefully other folks will chime in.