I’ve had quite a few similar problems. Mostly, my computer often presents an error message when I try to retrieve h9z files I have saved. Similarly, the same error message is presented if I try to email a saved (exported) h9z file to a friend.
My reliable work-around is to export lists to a dongle/thumb-drive and then attach those files to an email. For whatever reason that works. I can email to a friend and also import them back onto my own computers.
My computers both run Win 10 and a friend has some kind of Mac.