When looking at the metrics for a service, e.g. from Analysis | Resource List | Service we can see that over some time periods, but not others, not all service steps for the service are shown even when the steps are all required for a service and the Service Count metric is non zero, i.e. more than 0
It may well that only part of the service was "hit" during the period shown, so you may see this behaviour particularly if the service count metric has a low value
"Hits" on the service are hitting the service timeout
Product defect FXM-186
To eliminate Cause 1 increase the time period for the service metrics, e.g. from an hour to a day.
To eliminate Cause 2 increase the Timeout of the service from Configure | Application | Services in the FxM web console (the default is 298 seconds)
If neither of these workarounds resolves the issue it is likely you are encountering the product defect shown above under Cause 3
Waiting for fix in a future release of FxM.