high space usage after ext3 btrfs-convert

[koraynilay <koray.fra@gmail.com>]

Hello, I btrfs-convert'd a 475 GiB ext3 partition which had a few GiBs 
free, after the conversion I removed the /ext2_saved subvolume and 
balanced the fs but the free space went to 0 B (statfs, df) and 1.61 GiB 
(estimated) and the df value would randomly jump from 0 B to 1.61 GiB 
for a few seconds.
Here whenever I tried to do any more balancing it would just fail with 
ENOSPC.

So I made a 488 GiB partition on another HDD and added it to the fs so 
that I had 488 GiB free, but when I deleted ~215 GiB, the free space 
wouldn't change.
I tried to balance a few times with different percentages but the free 
space would always stay at around 486-488 GiB.

So I did a defrag of the whole filesystem (using the command in the 
btrfs-convert man page), which made the free space go down to ~200 GiB 
and after deduplicating using bees (until it finished) (there is a lot 
of duplicate stuff) the free space settled on ~370 GiB.
Now the used space (according to btrfs filesystem usage) is ~600 GiB and 
btdu reports there are ~282 GiB of <UNREACHABLE> space which should've 
been fixed by the defrag (according to what I found online).

A normal ncdu scan says there are 380 GiB used (402 GiB apparent).

Is there anything else I can try to fix it or should I just save the new 
files, restore the ext3 backup and redo it?

Thanks in advance.