Sometimes CallKit doesn't send back audioSession didActivate

I'm having problem with my VoIP application. My app uses Callkit and VoIP push notification to make SIP calls between same app. Sometimes after taking the phone the call doesn't start. I found out iOS is not sending back audioSession didActive response to my app. Is this known issue or bug?

Sometimes CallKit doesn't send back audioSession didActivate
 
 
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