When using btrfs send and receive to transfer a subvolume, file attributes (set with chattr) are not copied. I tested this with the 'C' attribute on a directory, which was present in the original subvol, and in the RO snapshot created for use with send, but not in the snapshot created by receive.
This is a known problem and will be addressed in v2 of the send/receive protocol update. https://btrfs.wiki.kernel.org/index.php/Design_notes_on_Send/Receive#Send_stream_v2_draft
Partially implemented in send v2.
Could you please elaborate the "partially" part a bit? So that we could know what to expect (to be still missing).
The protocol v2 now has a command to send the inode attributes/flags (compound name for the chattr/lsattr bits and also for the newish XFLAGS) and the command is also generated when v2 is used. The receiving side does not apply the flags yet - that's the missing part. In some cases it's not yet possible (lack of interface, like turning on/off the NODATASUM bit), not directly applicable (setting NOCOW on a nonzero file) or tricky (with IMMUTABLE and APPEND bits no changes can be done to the file so they'd have to be unset temporarily). Now tracked in https://github.com/kdave/btrfs-progs/issues/526.
Thank you!