This informational warning of Cannot do (something) while a transaction is in progress is because there was an attempted action that took place on an item or customer profile after the store landed on the Transactions screen, even if the item that was edited wasn't in an active transaction.
In the below gif, I run into the warning when I attempt to edit an item in the Active Loans screen from the customer's profile after I started on the Transaction screen.
To be able to make edits on the item you can just hit the Home button on the top left of Bravo (confirm you want to leave the screen).
Instead of going to the Transaction screen when looking up the customer (by hitting enter on the keyboard or choosing Select or OK on the Customers Found window), hit View to be taken to the customer profile and adjust the item information from here.
