I've ran into this with my azaleas..... had like 5-6 I was growing on pots from a nursery. Still haven't got the problem quite solved but here I things I've found.
1. azaleas hate stress and can't tolerate much, must be kept outdoors, and need acidity in the soil, ph is important.
2. they also HATE being pruned much. they don't respond well, if growing it in the ground for a bush.... most say to never prune it.
3. DONT EVER EVER fertilize your azaleas when it is looking sick. This may have been the problem, lightly and less frequent with azaleas and fertilizer.... and must use the acid kind
4. Depending on the timeline.... it may actually be a nutrient deficiency.... can't quite remember... but iron I believe is what causes that, but a few others do as well.
My best guess is you combined: root and limb pruning + fertilize (never after a root prune IMO) + repotting + wrong environment
Mine all died a slow death when this set in....