Note:
Photos will be selected based on the order they are in your file explorer. If sorting by date in the explorer, they will be uploaded by date. To upload by name, sort by name using the first column in the explorer.
Another option is to selected photos in groups, and they will be uploaded by within their grouping. In the attached example, I could select photos 1, 3, 5, 7, and 9 first. Clicking open in the file explorer will add these photos into the first group. Then I can select photos 2, 4, 6, and 8, click open again, and my photos will be sorted by odds and evens.
You must click the Update Photo Order button before changing tabs to save the order. If you click a new tab and go back, the order will be reset to the currently saved order. Always be sure to save your order after you've moved any photos.