Please see this photo. Today and yesterday, the dark rush suddenly stopped with, as you can see behind the pop up, all my players from team 3 still going strong, and even one enemy of this round still standing. I have rebooted between. I had been just looting, so not sure when this started, as I only decided to try and get my personal best up this week as it’s been a while.
There’s a limit at 110 rounds. Did you see how many you got to?
Today it stopped at 22!!
I suspect that is the number of waves, not the number of rounds. The number of rounds can be seen in the circle in the middle at the top of all battle screens. In your original screenshot it is hidden by the victory mark.
Sorry, yes, 22 waves. But I’ve happily got 30+ waves before 
Yes, the limit is 110 rounds. The enemies rotate each day and some of them has higher magical resistance so that could be the reason you get fewer rounds.