Introspection and overcloud commands fail on mistral after 1 minute with message cannot concatenate 'str' and 'int' objects in Red Hat OpenStack Platform 10

Issue

Introspection and overcloud commands fail on mistral after 1 minute with message cannot concatenate 'str' and 'int' objects in Red Hat OpenStack Platform 10

From the CLI:

[stack@undercloud ~]$ date; time openstack baremetal import --json ~/instackenv.json
Thu May 25 08:13:29 CDT 2017
Started Mistral Workflow. Execution ID: 9eb0f0cb-ad46-49c3-a315-4012407281e1
cannot concatenate 'str' and 'int' objects

real    1m0.841s
user    0m0.686s
sys     0m0.106s
[stack@undercloud ~]$ date; time openstack baremetal configure boot
Thu May 25 08:14:42 CDT 2017
cannot concatenate 'str' and 'int' objects

real    1m1.437s
user    0m0.698s
sys     0m0.110s

Running introspection with the --debug command, mistral seems to hang on Connecting proxy...

openstack --debug baremetal introspection bulk start 
(...)
Instantiating messaging websocket client: ws://192.168.100.76:9000
Connecting proxy...