Hoe did you add the photos to the shared album? Did you select them all at once in an album and share them together? Then the sorting in the source album will be ignored. When you are sharing a batch of photos at once, you have no control over the order the photos will be added to the shared album. The most recently added photos are always appended at the end of the shared album, so they are easy to find by the subscribers.
When you use the "Sort" command to sort a shared album, the photos will only be sorted on the device where you are currently viewing them. it will not change the sorting for the subscribers.
The older versions of Photos are stripping the capture dates from shared items, so it is not possible to sort the shared albums by the date taken.