MixMonitor B flag periodic beep cannot be heard once our server hits 50 calls

We are trying to use the MixMonitor B flag to play a periodic beep, but once our server hit 50 calls, we cannot hear the beep. We can see in the debug logs that the beep logic is being executed, but the beep appears to be too quiet to be heard. We have also tried with Monitor as well, and we experience the same issue.

Is this a bug? Or perhaps there is some sort of volume setting we can change?