Service Broker Error - The conversation handle is not found
You might want to try Microsoft's built-in ssbdiagnose utility.

The ssbdiagnose utility reports issues in Service Broker conversations or the configuration of Service Broker services. Configuration checks can be made for either two services or a single service. Issues are reported either in the command prompt window as human-readable text, or as formatted XML that can be redirected to a file or another program.

And possibly specifically this part:

To correctly analyze the configuration used by a conversation, run a ssbdiagnose configuration report that uses the same options that are used by the conversation. If you specify a lower level of options for ssbdiagnose than are used by the conversation, ssbdiagnose might not report conditions that are required by the conversation. If you specify a higher level of options for ssbdiagnose, it might report items that are not required by the conversation. For example, a conversation between two services in the same database can be run with ENCPRYPTION OFF. If you run ssbdiagnose to validate the configuration between the two services, but use the default ENCRYPTION ON setting, ssbdiagnose reports that the database is missing a master key. A master key is not required for the conversation.

Alternatively you might want to consider contacting Microsoft and opening a case with them.
Reference: ssbdiagnose Utility (Service Broker) (Microsoft | SQL Docs)