Backstory: I currently have a BH Ultralight RC road bike that I use to ride to work. About 6 weeks ago I took it to the bike shop because the pedal was slipping over the cassette when I took off, so they changed the rear cassette and the chain, and they did a few other things. It cost $220, but The bike was running very smoothly.
Then about a week the dropout (that's what they called it) literally snapped and the rear derailleur got stuck in the rim. I took it to the shop again, they straightened the "transmission" (what they said), they also straightened and reused the chain, they changed the spoke and they installed a dropout. I picked it up and took it home.
The issue is that I rode it yesterday for the first and the ride is terrible: the pedal's slipping again, the chain is always scraping something regardless of the shift, and it's making all kinds of noises. It's just terrible.
Since they said that the cassette and the chain was damaged from the dropout break, I'm almost sure that they'll want to change the rear cassette and the chain once again. My concern is that the dropout has never snapped like it did before (I didn't even know that existed), and I'm thinking that it broke because they didn't install something right the first time I took it.
Question: is it possible that the dropout broke because something wasn't done correctly when the new cassette was installed?