I was curious about Live iso reading BTRFS so i formatted a usb with it.
Had interesting results
All the current Solus Live read the usb just fine.
Fedora also
Garuda also
So that in my mind tells me his BTRFS IS MESSED UP (If i am seeing it right)
I am going to suggest this with (USE AT YOUR OWN RISK) label.
Burn a Gardu iso (I used Gardu gnome) in it you will find a program called (BTRFS ASSSISTANT)
which may be of help.
When you run it in lower left it shows errors see if it shows any for yours. (or if it can read it at all)
Above that is the disk info its looking at make sure its right.
Cross next bridge when we come to it.
you are prob more up on using btrfs than i am.
Best I got for now.
Note: Gardu might be handy iso if it works out for you to keep around since you are using BTRFS if this works out.
Also it appears with any live iso BTRFS is going to be read-only but that would atleast let you copy your data.