Encountered this with my Necromancer. When in town (this happened in The Outcast Camp) minions do not spawn, and will reappear once the player enters a zone with enemies.
I was able to use “Summon Skeleton”, “Summon Skeletal Mage”, and “Summon Bone Golem” outside of town, use a way point to enter town, changed the abilities on my bar to not include any summons, and when I used a waypoint to return to The Risen Lake I still had all of my summons following me. They would engage enemies as normal.
When I changed my ability bar to put “Summon Skeletal Mage” back on it all minions except for the Skeletal Mages disappeared.