I was able to reproduce this scenario using the sample application on iOS as well as my own application. I have the settings in the zoom supplied iOS sample app as :
[[[MobileRTC sharedRTC] getMeetingSettings] setAutoConnectInternetAudio:YES]
[[MobileRTC sharedRTC] getMeetingSettings].enableCustomMeeting = YES
Usually the first time I run the app connecting to the desktop application hosting the meeting, it works as expected, audio connects and works. After disconnecting and reconnecting to a meeting again I’ve seen the audio type switch from VOIP to None via the onSinkMeetingAudioStatusChange in CustomMeetingViewController+MeetingDelegate.m which in turn calls BottomPanelView:updateMyAudioStatus where reading the audioType via [ms myAudioType] returns MobileRTCAudioType_None and sets the icon for the audio button to ‘icon_meeting_noaudio’. Tapping the button will then prompt for the type of Audio connection and connect correctly upon choosing the type. I was expecting this to not change.
You can also watch the ‘microphone’ icon disappear for the newly connected user in the Zoom desktop application if you have the ‘Manage Participants’ side panel open. The new user will appear with the microphone icon and video icon visible, but when this issue happens the microphone icon will disappear very quickly after you see the user appear (this is when you get the audio status change in the iOS SDK sample app).