Only managed computers can be added to scope for Configuration Profiles, Policies, Managed Preferences, etc. Just because it shows up in Inventory does;t mean its actually managed.
Check the management information and status for the Mac by looking under the General section in the computer's details.
Here is a random question, do you have any special characters in your management account password? I know there is an issue where if you have any special characters such as "! @ # $ %" will break management of your computer. You can go into the computer record inside the JSS Web Interface and reset the management password to what it is supposed to be and management will work correctly.
Have you run a "sudo jamf enroll -prompt" to attempt to re-enroll the unit?
Take a look at the computer's inventory record to see if it shows up as MDM Capability: Yes. If it doesn't say yes it will not be shown within the scope options. A couple of items that get missed sometimes are that the Computers must have OS X v10.7 or later and a Recovery Partition. Hopefully this information helps.
It is one of those things that has popped up since 8.6.x. We always get caught with it. If you enroll the computer using "sudo jamf enroll -prompt" you should be able to enter in the information as requested in terminal and then go into the computer record in the JSS and just re type your management password without issue. Then it is just a matter of getting the machine to check in.