This seems like a bug in Gen 9 and has happened to me a few times now.
I have a table called y_cat_req_junction which has 2 field. 1 is a relation to ticket and the second is relation to an extratable.
After creating the table and populating it with some values I tried to group by a field, and now I cant see anything when I click on the table. I can add values to it by CRMScript and make selections on the table but not see it...
Also, if I try to create a new entry in an underlying related table which only has 1 field, that field wont show when creating a new entry.