Dropped calls at voicemail

We are having a bit of an issue with our PBX system. Some of our users are reporting outbound calls being dropped every once in a while as soon as the recipients voicemail message begins. The system will say “Call cannot be completed” “The number is not answering”. It is different every time. I took a look into the CDR reports and found out we are having about 2-3 dropped calls a day. They are all the same in terms of their event process however I did notice that they do not initiate a BRIDGE_START and a BRIDGE_END as opposed to successful calls. Any help would be greatly appreciated and I can provide more information if needed.

Detailed view of one of the dropped calls. They are all the same.

Every dropped call has a disposition as “failed” and the app column always says “Congestion”