Cannot read properties of undefined (reading 'error')

Question

I labeled five documents. Each document has many pages, but I labeled only a single page of all five docs.

When running the train command from Form Recognizer Studio, I am getting the error: Cannot read properties of undefined (reading 'error'). Any lead as to what is causing this error? Many of the labeled columns having single letter values (such as Q, M, A). Many of these letters were initially recognized as Checkboxes: Seeing some values as checked (for values of 'A') and unchecked (for values of 'Q'). Could this be causing the 'undefined' error?

Thank you for any help in advance!