CRS are renowned to being sensitive, sometimes the quality of the stock may not be good...
Your staurogyne has been grown emersed, it doesn't grow as tall grown submersed, so all tall stems have been grown out of water. Staurogyne is one of those plants that is almost always grown emersed, and as the Tropica website say's you will almost always loose the emersed leaves.
During planting in the aquarium, the longest upright shoots should be cut off and each pot should be divided into 2 to 4 pieces which are then planted close to each other in a small group. The emergent leaves will eventually die-off when under water and these may also be removed during planting. By doing so, the low compact growth form is maintained. In the aquarium, Staurogyne repens develops new horizontally creeping shoots from the plant basis which soon form a beautiful carpet. The ability makes it an ideal plant for the foreground.
As before, you can either give it a good hack back or do what you did with the Alternanthera, it takes a while to take off, but when it does it looks ace. Mine at present is just starting to take off.