Sorting not working properly

Trying to sort a sheet alphabetically by a single column. Most of the column sorts alphabetically, but some values do not. Examples: In one Smartsheet, I sort by customer name. All customers sort correctly except for three which start with N and go to the top ahead of customers starting with A.

In another Smartheet, all customers sort alphabetically except for a group of 20 which drop to the bottom and then start their own alphabetical list. Case (upper vs mixed) does not matter.