A board cannot have a row of a shared relationship

I have entities of type Page and Book. Both have the relationship to a database called ‘Priority’.

If I want to create a board with a mix of pages and books, the Priority field that both have, cannot be selected. Instead, only the field ‘Created By’ can be selected.

Is there a workaround for this issue?

Does the priority field have the same name and cardinality in both dbs?