We can get recovery message when xpanes works with pipe on the out side of tmux session.
This is expected behavior, but ...

$ seq 3 | ./xpanes
xpanes:Warning: Attached session is required for 'Pipe mode'.
open terminal failed: not a terminal
xpanes:Recovery: Execute below command line to re-attach the new session.

tmux -S /home/docker/.cache/xpanes/socket.5840 attach-session -t xpanes-5840

tmux -S /home/docker/.cache/xpanes/socket.5840 attach-session -t xpanes-5840 does not work because /home/docker/.cache/xpanes/socket.5840 does not exists.

$ tmux -S /home/docker/.cache/xpanes/socket.5840 attach-session -t xpanes-5840
no sessions

This is caused by the previous changes released at v3.1.1. Socket file is automatically deleted when the process exits.

It should be fixed next release.