Considering that we are about to start Summer, that the plant came from a greenhouse with perfect sunlight/humidity/etc conditions, that newly transplanted hydrangeas have transplant shock for a while and considering that its watering regime may need a little tweaking as time goes on, it is not surprising that we may see that happen often now. I was going to add another item to the reasons above but I could not see the bottom of picture 2 clearly: does the plant have organic mulch? If not, maintain 2-4" or mulch year around (no rocks). This helps minimize soil moisture evaporation and protects the roots from cold/heat extremes. fyi only: paniculatas are known for "showing their feet" when the weather starts to get hot.

The root system that the plant has is not as large as it used to be so you may notice that the plant gets heat stressed often during the worst days of summer. This usually means when temperatures are 85F or more. It can also happen when the soil has too little moisture or when it is very windy. Feel free to provide extra shade if it complains a lot during its first year. You can use outside chairs and umbrellas to provide extra shade this year only.

Make sure that you have started watering at Summer time levels. The amount of water per watering should get the soil all around the plant moist down to a depth of 8" or so. Water early in the morning (6-8am) if you use a sprinkler so the leaves do not stay wet for long periods of time. Water only the soil, from the crown (the area where all the stems originate from) outwards in all directions.

To see if it needs water, insert a finger into the soil to a depth of 4" (that is where the roots normally are) and water if the soil feels dry or almost dry. This time of the year, I water about 1.5 gallons of water per plant but test the amount needed using the finger method: water as usual; then insert a finger into several places around the plant to a depth of 8" and see if they feel moist. If not, use more water.

I’ve added mulch as of today to all of my beds, and will try your recommendations. Thank you!

that the plant came from a greenhouse with perfect sunlight/humidity/etc conditions,

What makes you think that?

focus on the growth tips ... if they look good.. you are probably all set ...

interior or older leaves .. can be sacrificed .. for lack of a better word ... when in high stress .. like after transplanting ... that is is only such ... that we declare it minor stress.. and just water properly ..

when the future.. the new growth is doing this... is when its not looking good ...

water properly.. and be an optimist ...

your arent a green thumb.. until you have killed every plant 3 times .. so whats to worry about ..

ken