jBPM process stops at the middle of process

Issue

We have a customer order process which has been working fine for several month. It suddenly is showing inconsistency. Some times it executes the whole process, some times it stops at the middle of the process.

This order service tries to execute different services in the ESB. This problem happens when jBPM calls an ESB service, The response from that service comes back but jBPM does not resume the process. If I manually signal the process via jBPM admin console it resumes the process.

There is no error in the ESB log.