Dynamic form multiple items

[RokiRomero]

Hi, I have an app for loans and tool inventory.
I have a Loans table and a Loan Details table.
At first, I referenced the Loans table from the Det_Pres table with the "Is Part Of" checkbox.
This allowed me to add multiple items to a loan for one person.

But out of nowhere, the field disappeared and no longer allows me to add any items.

Has anyone had a similar issue or know of any other way to incorporate this feature into my app?