I am experiencing the same bug (ubuntu 18.04) fdisk shows correctly the partition table but not gparted (or it seems blkid, in my case util-linux 2.34 14-Jun-2019). The whole disk /dev/nvme0n1 is TYPE='zfs member'.
If that can be useful I noticed this bug was not present went the zfs partition was freshly created by following the instructions on https://wiki.archlinux.org/index.php/ZFS. A launch of gparted after the zpool create showed properly the partition table, even flagging as zfs type the new pool It appears only after enabling the automatic zfs mounting on boot, and rebooting the machine.
