Debug output from the latest patch attached. Here's the error:
BTRFS info (device dm-3): clone: -EINVAL other, src 400186 (root 2792)
dst 400186 (root 2792), off 79134720 destoff 79134720 len 4751360 olen
4751360, src i_size 83886080 dst i_size 83886080 bs 4096 remap_flags 0