User picker does not work on reopened forms

[Paul Fechner]

I have a form used as part of our leaver process within Jira Service Management.

The form contains a single person picker and has no automation behind it.  It is very vanilla.

Through the customer portal, the form works perfectly when creating the initial request.  All of the fields work as expected.  However, if they edit the form and then try and edit the data within any of the person picker fields it says "no matches found".  It is as though the field is not being populated with all of the people accounts.

Editing the form within the agent view works no problem.

Is this a bug or a permission issue?