I don't know the answer, but like zenkatydid asked, does a tiger lotus, or any other plant, go into dormancy similar to what normal plants do? That may explain the action of your plant.
Also, has anything else changed in the tank? Maybe the plant is stressed?
75g FW Planted Community; 55g African Cichlid
29g Biocube SW Reef;12g AP Mantis Shrimp/Brittle Star
2 Cats, 2 Dogs, 5 Turtles