Issue:
When selecting multiple values in a string field, it only shows 300 entries in the 'Select...' window.
NOTE: This is expected behavior, we have limited the number of records to show to 300.
Workaround:
If there is a value that is not in the 'Selected Values' window, you will need to start typing in the 'Select...'field so the autosuggest will start to filter the values, whatever value that is not already selected in the 'Selected Values'window, will show up in the 'Select...' window.