A ministry is missing from the Scheduling Options > Ministers Needed area (and is therefore not getting scheduled in the auto-scheduling), while they are still showing in the Configuration.
If Ministers needed are not displaying from the Ministry Scheduler > Scheduling Options > Ministers Needed, the display must be reset.
To reset the display:
Go to: Configuration > Select the applicable Group > Select the Applicable Event > Select the Ministry > click the edit (pencil) button > Click Save
Repeat this for any other missing Ministries.