Custom store permissions
When working in a hardened environment you can’t see the tuning packs in your custom store.
Hardened environments sometimes modify the members of system groups or change the default Access Control Entries (ACEs) on the file system Access Control List (ACL). In a normal Windows directory we would expect that the System, and Administrator group have Full Control ACEs with Authenticated Users having a Modify ACE.
Check the ACL on your folder to ensure that your console users have at least read access to your custom store (Effective Access under Advanced in a Windows based directory is a great way of quickly verifying this). If you do not wish to use groups like Authenticated Users, an ACE for a local group, Active Directory Group, or explicit user would also do the job.
If there is only the Administrators group (and a requirement for this) in the ACL you can also use the 'Run as administrator' option when launching the SCOM console to elevate your context and gain access to your custom store.