I'm actually glad to hear someone else having this exact same problem lol. My supplier switched to Bridgeport fittings a few months ago and they've been awful! I always used the steel fittings, but with these, you got to back out the set screw, and the things won't tighten against the box! Also I noticed the steel fittings are made in Thailand. So I switched to the die cast versions from Bridgeport, made in the USA, they lock down on the box by hand, and the set screws are ready to go. I've seen the die cast fittings broken, but only because something else worse happened to break them. Bridgeport's rain-tight fittings are bad too. They come with a giant rubber O-ring that you can't tighten down real tight or the O-ring will squish out, there's no "good enough" amount of tightening that the fitting stays put.
The ones we got before were EGS or IGS brand, can't remember the name, those were good!