When a pmm is no longer visible in Calibrator it is possibly deleted.  Deleted pmms are stored for about 90 days in the Hub Trashcan before being permanently removed. 

- Go to app.printfactory.cloud  -> Resources -> trashcan

- Find the pmm and select the cog at the right hand side and select Restore.  
This pushes the pmm back into the Calibrator of each installed seat.