Import/add previously used TrueNAS disk (zfs_member)

If it doesn’t work with the GUI, you probably need a reboot, then see what the status is - and if necessary export it again from the GUI and switch to trying to get it working from the command line - because from the CLI you have a lot more options to deal with recovery situations.

Assuming you can get it imported and functioning correctly from the CLI, you can then export it from the CLI and import it again through the GUI and you should be good to go.