Manually importing a FreeNAS Jail

I just had this same issue today and came across your post.
The reason mine crashed was because the plugin i was importing was huge (about 10GB in size).
–What i ended up having to do was manually create a dataset. Im using plex as an example.
zfs create zpool/iocage/jails/Plex
or use the GUI
–Then unzip the file that you got from your export. I unzipped it to the iocage/images folder. you should have two files, one the same name as the zip file and one with _root added to the name.
–Next i had to import the data from the unzipped files.
zfs recv -F zroot/iocage/jails/plex < plex_2019-10-30
zfs recv -F zroot/iocage/jails/plex/root < plex_2019-10-30_root
Once you do this then you should see it in freenas in the jails section. It came up as if nothing had ever happened for me. Hope this helps anyone else that came across this.
as i was also changing pools i had to edit the fstab file in the jails/<jail> directory