Summary: These question marks do not indicate an error at all. Move a basic text column to the very left of your table and notice what happens.
When you create a relation or a query, each item you see in a cell represents an entire row, and Glide picks one of the columns of that row to show what the row is. It will start with columns at the very left of the table. If your table has a RowID column, the relation/query elements will be represented by a RowID. If you table has a text basic column at the very left, it will show that. But if you don’t have a basic column at the very left but a computed column or something more “exotic”, it will show a question mark.
I used to know the exact rule, I forgot it, and most of my tables have RowIDs so my relation/query columns don’t show question marks anymore. But long story short, the question mark you see is not an error.