Disk 1 is messed up some how. 6TB drive, with 484G used, but its 100% full (hence the errors)
/dev/md1 5.5T 484G 0 100% /mnt/disk1
If it was formatted XFS, then I'd say to check the disk file systems, but since its BTRFS, you probably should wait for @johnnie.black
(Or alternatively change the filesystem to XFS and then reformat the drive which will also solve the problem)