NetSuite does not allow concurrent global searches which is what the widget is doing when a search string is typed quickly since a global search request is sent on each key press. For example, if you search for SO123, it starts searching for SO1 (minimum 3 characters required), and then it will search for SO12 and then another search for SO123. It's possible that before NetSuite completes the search for SO1, it's already searching for SO12 which could result in a concurrent error.
As a best practice, it is recommended to type in the search string slowly to allow NetSuite to complete the search. Or if you are copy/pasting the value, you can also delete the last character and manually type it on the keyboard to initiate the search again.