You should find the callUUID of each participant of the conference call so as to debug.
You can find the call_UUID in below ways:
By checking your account dashboard logs:
Login to your Plivo dashboard from here https://console.plivo.com/dashboard/ and navigate to https://console.plivo.com/voice/logs/calls/ click on the timestamp of the relevant call which you want to debug, then you will get the call_UUID.
Using the get all call details API: https://www.plivo.com/docs/api/call/#get-all-call-details
To find the call_UUID for a certain call you can use this API by making a GET HTTP request to the call detail records(CDRs) which will result with information about calls along with details about each call.
After getting the callUUID, navigate to https://console.plivo.com/voice/logs/debug/?next_id=&page=1&type=all and input the call_UUID in the search field, you will get the details of the call like this
You could check the XML document which is used on the call to handle the call flow which will help you debug the call from your end as well.