Some of the stems have died off for whatever reason. Unlikely to be cold in your zone so possibly some sort of watering issue last season or over winter.

Since the plant has well developed flower buds showing, I'd just remove any stems that are dry, brown and show no signs of leaves now. Hydrangeas are caning shrubs and it will replace them eventually, as long as all other growing conditions are being met.

It looks like your plant has accumulated several years worth dead stems that should be pruned all the way down. This is causing new stems to grow around those old stems, which results in the stems and foliage spread weird and growing like this.

It is ok not to want to prune but I would make it a habit to always prune those stems that do not leaf out by the end of May. After one or two seasons, evaluated how the stems are growing with none of these dead stems and tweak things so the plant looks more to your liking.