I have a 'Michael Hill' from the same Polly Hill series of groundcover azaleas and unfortunately this is the nature of the beast due to Rhododendron nakaharai parentage.
I'm in z6 and all three plants that I have losing foliage on all but most lower branches at the end of the winter, though they were fully evergreen till February-March. They will not grow new foliage till the end of the May and will bloom very late, for me in July.
Plants look like they are completely dead, but in fact if you snap the branch you'll see the green tissue.
They are planted along driveway and are highly visibly, so I have to move them somewhere where 'dead' azaleas wouldn't bother me everyday from March till June.

I have a MH and I thought it was my siting it where I did (nearly full sun) and later putting in a short slate step thru (the bed) with radiant heat from the bluestone 'cooking it'