Is your sceduler account running, and configured as an Admin?
I have the same problem.
I create a OSD Task and drag&drop a device to this task.
The scheduled task shows Quantity = 1, but the device isn't in the task.
This only happens with a specific device.
we run LANDesk 8.8 SP2
In the Network View, check if the missing device has an IP address. I used to see that in 8.7 occasionally.
We just upgraded to LD9 and are now seeing this issue. Sometimes, dropping 10 PCs into a scheduled task, the "All Devices" number jumps to 13 and shows 3 listed as "Active", but clicking on the "Active" group shows nothing. It's a mystery machine.
We are seeing this issue also. PCs are showing but when you try to open the results or all devices no PCs appear.
I had also an Case for that, because of an Invisible Device in a Scheduled Task with LDMS9.
But after deleting the Scheduled Task, it never happens again.
So we closed the Case.
I also noticed a Patch for something similar, today: