I originally created a share named “media_tank” but when I then created a share named “tank” it made the subvolume “media_tank” = the same as the first share I created.
I deleted both “media_tank” and “tank” and created “media” which has subvolume “media” as expected but “media_tank” and “tank” re-appear.
You can also update to 5.0.13-0 in the testing channel, which has fixed a few more things. It’s really close to the next stable release as mentioned by @phillxnet in other forum threads. However, otherwise follow @Tex1954’s hint.