This might be the same problem I just ran into. There's either been an update with the plugin or with MZ itself. The plugin now requires an extra switch to verify the spawn success; I named mine <Self>Spawn Success - I only just figured it out minutes ago so it isn't specific yet, and edited step 3 of the plugin command.

Caz - your current template doesn't need it to work, but when we c/p the template this new third step is automatically added in.