To understand why a plant is not performing, sometimes we have to look first at its required conditions:

Hydrangea paniculata 'Jane' known as Little Lime Hardy Hydrangea requires part sun to full sun, which means it needs at least 5+ hours of sun each day. It is best grown in Zones 4-7 in organically rich, medium moisture, well-drained soils. For best foliage and blooming, apply a controlled release fertilizer in early spring such as a 10-10-10. A supplemental dose of liquid feed can be done in mid-summer. It has moderate water needs and prefers a consistently moist soil—but again, it must be well-drained. To best determine if the soil is consistently moist, use a houseplant water meter to check soil moisture. Make sure it is properly planted with the root ball above ground level, and never place mulch all the way up to the base of any plant. Grower information shows that Little Lime blooms on new wood, which means you will need to prune the shrub in early spring. Below is the CSU guide to pruning flowering shrubs:

https://static.colostate.edu/client-files/csfs/pdfs/PruningFloweringShrubs_619.pdf

As far as the problem with the leaves, it does not appear to be any of the common foliar disease seen in Hydrangeas, but rather, a reaction to something environmental on a select few leaves. It takes roughly 12-18 months for a new shrub to become completely established in the landscape. Until establishment, plants will react to a host of things both above ground and below ground. The newer growth does not have any foliar issues, so perhaps something happened a couple of months ago that caused the damage. Exceptionally hot weather, dry soil, overly wet soil, lack of nutrient uptake, water (or chemical or dog urine) splashes are all reasons why Hydrangea leaves yellow, but it is difficult to determine what it is in this instance. Especially since there are only a handful of random leaves that are affected, it is likely not a systemic issue. At this point, remove the damaged leaves and continue to monitor the plant for symptoms and determine if it is getting its required conditions (above).

As noted above, grower information shows that Little Lime blooms on new wood, which means you will need to prune the shrub in early spring. If you did prune, and depending on when you pruned, the quick freeze in April had adverse effects on plants. Many buds froze so some of our favorite blooming plants were unable to produce flowers this year and are struggling to establish and grow.