I could not make out the affected parts up close but they appear to be browned out. Browning of the blooms in the summer on the first 1-3 years suggests that the shrub may need more water. To help dissipate the heat from blooms and leaves, some people temporarily give them shade in the form of a lawn chair or umbrella. In future years, when their root system has grown bigger and can absorb more moisture from the soil, this may not be a problem. If the plant does not get enough moisture, the plant begins to kill the blooms (what you see as brown out) and the leaves could be next. The leaves may show browning of the leaf edges that moves inwards. I noticed some leaves that had been eaten. It does not seem to be a problem (yet) and I would ignore it but, you may want to keep an eye on that and look for pests during the day and night, especially if that problem is growing. Lastly, keep an eye on a gray mold that sometimes makes the blooms look as it they were wet, then they turn brown and you see this mold. I doubt your shrub has this but it pays to keep informed just in case.

Mine is still small but for a year 3 it has a lot of flowers. People have commented on it's arching habit and it's been suggested a raised 'bed' would give it the height it needs so the branches don't drag on the ground. I planted mine on top of a retaining wall that is 4 feet off the ground with that in mind. It's branches are already arching down significantly

Yes, see this link: https://www.houzz.com/discussions/strawberry-sundae-anyone-dsvw-vd~4754011?n=26

Starlight, do you have a wall that you can plant this at the top of or can you place it a raised planter? There are some panicled hydrangeas that don’t have strong enough branches to support the huge blooms, including both Strawberry Sundae and Vanilla Strawberry, so planting to take advantage of the form may help. You can also consider removing the lowest branches or adding support prior to leaf out in the spring so that it gets camouflaged by new growth. I don’t much like this form, so I choose other varieties. If you have been pruning it, consider not pruning and deadhead when blooms fade. In general, old wood is more rigid than new wood, though with SS’s over-sized blooms, there will still be arching. Leungkitty, yourLittle Lamb may be in too much shade or it may just be young. Where I am they do great with all day sun, though farther south the flowers last better with shade during the hottest part of the day. Your spot looks like there is a lot of shade.