Begonia 'Harmony's Stormy Sunset'

For two years, I grew this grouped with 3 or 4 other begonias on a large pebble tray. It grew vigorously, the stalks were 12-18 inches tall, it got an hour of direct eastern early morning light and was in indirect bright light for the rest of the day. Kept the soil barely above bone dry with a deep bottom water once a week. It was gorgeous and easy to care for. A bit after the 2 years mark, it just kind of stopped growing. The leaves were all still healthy, it had no pests, I didn't change my routine, but one by one the leaves died off until there were none left. The rhizome (?), roots, were still healthy and plump, so I kept it in the same spot and watered just enough to keep the dirt barely damp. I was hoping it'd come around when spring came. Once it did, I fertilized at 1/4 strength. Alas, it didn't bounce back. I know some begonias have a short life. I think this one must be in the 2-3 year range. It sure was gorgeous and easy while it lasted! (BTW, I live in a dessert, but with the pebble tray and grouping, this and the other begonias did just fine.)