hello everybody,
I know that post is more than 2 years old. but I am having the same issue with two SSDs as RAID1 (as external USB Disk) for my SBC.
on the USB Disk is BTRFS used as fs and while I just copied data yesterday it became slower till to the point it just stuck and didn't respond.
My Linux system went in recovery mode and I can neither mount the disk nor do any of the check and rescue etc.
Basic error message is always No valid Btrfs found on /dev/sda.
In gparted it shows me that I am using 93 GB out of 450 GB. So this information is being proper shown. also the details are being shown properly in gparted. I will try doing more troubleshooting before I reformat that disk.