Actually, it is better that you do not disable the trunk, just leave it as is and start the packet capture. You do not really want to alter the state that the UCM is in while the problem is occurring. By disabling and the re-enabling. you are forcing the UCM to re-attempt the register request manually and Ideally you want to be certain that the UCM is attempting to register on its own without artificially inciting the action. If you left the default values the request should come approximately every 20 seconds.
Also, you do not need to change the password if only sending a capture file. While the password will be in the messaging it will be encrypted by virtue of the nonce. The nonce is the key that allows the other end to decrypt and the nonce value changes every time a message with the credentials is transmitted. nonce = number once. Rest assured the password is not sent in the clear. I am just trying to prevent the possibility of having to contact the provider to change the password. Some providers assign it and they are the only ones who can change.
Not knowing what version you were on before the upgrade might play a factor as if an earlier version, then there have been a number of changes since, that might be responsible.