I felt this way with old school runescape but could never prove my superstition.
Sometimes you raid for 30 hours and get nothing. Other times you get 5 drops in 3 hours.
Sometimes you killed Bandos and his first drop was tassets... then a few more drops... the drop changes from one tick to the next. If you got on the right cycle, you leave with many drops. If you're not on time, you get nothing for 10 hours straight. No way of determining when the right time to kill is, and even if there was, sometimes you have shit dps and take 2 minutes to kill. Other times, he's gone down in 2-3 hits from your squad.
I think it's random but it's more fun to think you can influence RNG.