Thanks for your good advice.I did a minimum sound test, only a few sound played at once but the sound lag still happens just like what Allenheathx said. I think the sound lag is not caused by too many sound playing at once. The lag will always happen after a while of playing.
I think it is a memory leak when the engine running on iOS. The lag happens when the audio memory is full and starting to recycling. Normally it will not cause sound lag. It must be something wrong. And it is engine related, remember we won’t have this bug on 4.22 to iOS12 on the same project.
I still working on this bug. And I will make a demo to show how this bug happens. I am not a engine level developer for UE4 so I can’t debug this for the community. Only thing I can do is reveal.
How could a UMG widget affect audio engine, it’s weird. And I must have a widget in my game. I will test it.