I would do this:

1) Run concurrent manager purge program and purge all data:

Purge Concurrent Request and/or Manager Data

If the program is not run by the manager manually delete data from tables:
FND_CONCURRENT_REQUESTS and
FND_CONCURRENT_PROCESSES.

(Take database or virtual machine backup as there is a risk)

Restart all services and see if that fixes the problem.

2) Next I will run Concurrent Manager clean script
following the instructions in Metalink Note:134007.1

cmclean.sql