I have no idea if it was a system failure, but there was an instance when I lost a bonus round because the game crashed mid-spin, and after I refreshed the page, it's like that spin never happened.
That kind of manipulation is hard to prove, though i've gone through a similar pattern where they'll go cold later on after you get your first few wins, and your bankroll will struggle since it can't survive hundreds of spins.
I am interested in your case. Did you do something when it happened, like reporting or submitting a ticket about that problem? What about the bet history? Does it clearly say you got that bonus round? I am not really aware of the bet history tab when I play, I don't know if the bonus round is visible there.
I have never had an internal failure experience, only laggy play, like when you auto spin, then at a certain spin, it gets stuck or laggy. When it happens, I feel like my bet is being manipulated. The other problem that usually happens to me is just connection issues. I know this is not the casino's fault, but it’s really annoying when you get a double bet, the exact same bet.