No Snapshots but takes up half my drive!!!!

I have seen posts where a specific firmware upgrade caused some snapshots to become "invisible".  Unfortunately, I don't remember the details.  You can search the forum or wait for another reply on this aspect  But that may not be your issue.

Did you recently delete a large number of files or one large (probably fragmented) one?  If so, your problem is likely that the default balance is not a very aggressive one (it's dusage value is obviously low).  This is a problem I had when I migrated a lot of files to another NAS.  Over time, the system will probably reclaim the additional space.  But if you need the space now, the only solution is to SSH in and do a balance with a higher dusage value.  I have suggested that the GUI balance function have an option for how aggresive (and therefore CPU and RAM intensive, potentially locking out other functions) a balance will be.  One thing that's nice about initiating the balance from SSH instead of the GUI is the ability to pause it if you need better access.  That wouldn't work via the GUI well because the GUI is one of the things typically locked out.

While I agree that Netgear needs to do better testing, the second issue listed above is not caused directly by anything Netgear has written except that they have given no options for dusage in the GUI.  It's inherent in BTRFS.  I do not know if the first is something Netgear caused or is caused by an update of BTRFS that was included in an OS upgrade.