Just to make sure. Are you copying to your ZFS pool directory or a dataset? Check to male sure your paths are correct.

Push vs pull shouldn’t matter but I’ve always done push.

If your zpool is not accessible anymore after a transfer then there is a low-level problem here as it shouldn’t just disappear.

I would installe tmux on your ZFS system and have a window with htop running, dmesg, and zpool status running to check your system while you copy files. Something that severe should become self evedent pretty quickly.