Problem with audio earplugs new screen

Im new to zoom i take class with it so i use headphone with mic. Works fine but when the teacher put js in classes smaller groups temporarily to work on things, so new screen comes up suddenky i have no hearing. Then i just click some stuff and headphone in and out  thill i hear again. But then i go back to teachers zoomclass again temporarily no sound i do headphones out and click some stuff sound back. I dont understand why i prefer headphone j can hear people better but when that happen i have to put the headphone out to hear again why?