This happens when the workflow fails due to DAGMAN_LOG_ON_NFS_IS_ERROR when the submit dir is on NFS. It looks like this may have been triggered by an RPM update and a changed Condor default. The dag.dagman.out log contains:

ERROR: log file /path/to/workflow-0.dag.nodes.log is on NFS.

The workflow starts, and some tables in the DB get populated, but no jobs are submitted. In particular, the job_instance, jobstate, and invocation tables are all empty.

pegasus-analyzer
Traceback (most recent call last):
File "/sw/redhat6/pegasus/4.5.3/bin/pegasus-analyzer", line 1572, in <module>
analyze_db(options.config_properties)
File "/sw/redhat6/pegasus/4.5.3/bin/pegasus-analyzer", line 1021, in analyze_db
unsubmitted = total - success - failed
TypeError: unsupported operand type(s) for -: 'int' and 'NoneType'