Can't delete orphaned snapshots on ReadyNAS

Hello,

I run my ReadyNAS 516 as a simple X-Raid home movie server, so maintenance is somewhat low priority since there isn't much in and out action going on. My CLI skills are basically non-existent and all commands I look up on how to use them first, on this forum and googling 'how to' ... so none of this trouble-shooting comes natural to me.

The space has been steadily been declining and even though I would delete some files here and there, space would not free up.

I have about 11TB total and when it was at about 9.5TB full I started some deleting ... lots of it, at least 1TB.

I ended up with less space than before. OK, so I started deleting snapshots ... even less space. I disabled snapshots ... less space still.

balance, scrub, defrag .. multiple times.

disable quotas, re-enable quotas

I currently have 234GB of space left and it still shows like 1TB worth of snapshots allocated. (yellow on the pie chart, but 0 snapshots in the WebUI snapshots section) On top of that, it reported Data DEGRADED, but that was Disk 6 and that went away after a re-sync.

I used SSH to look into it directly and sure enough  btrfs subvolume list /data  shows a ton of snapshots about a year old. 39 to be exact.

I tried to  btrfs subvolume delete /data/VOLUME/.snapshot/1084    (with 1084 is one of the snapshots)

this gives me ERROR: Not a Btrfs Subvolume: Invalid argument 

I tried with rm , which tells me that it's read only ... but I'm logged in as root and it's rwxr-xr-x (I tried chmod to 777 and it tells me the same thing, can't change it because it's read-only)  

I don't know which logs are important, so here are all.

https://www.dropbox.com/s/x51uoie1ktccxqf/System_log-MiniPlex-20190615-191631.zip