I'm no expert, but that pot, whilst being nice and deep, is very narrow across for the size of the plant.
Has it been flowering?

I've had one in the same pot for 15 years and just feed and water it. We've never failed to get an excellent display and it seems very happy situated in the shade under my big magnolia.

Its small rootball might not have been able to supply the plant with enough water during the drought? Agree with Pb, try a wider pot too. Fresh compost will help as there will be hardly enough in that pot to feed a plant of that size for long.

As above. Roots of Rhody’s are wider than deep. Get some Erica eous compost, and repot it in a wider, shallower pot. It will be fine, it looks good and strong!