Yes, too much sun "can" be the problem, that is why asked how much sun it had. Many of those plants are developed under wholesaler greenhouses, whose leaves are not quite exposed to direct sunlight there so when you bring them home, they leaves are shocked and need to gradually "acclimate". Most times, they can go from the plant nursery to your patio but sometimes they pout. Ironic as this hibiscus can normally handle full sun. I had several hedges of tropical hibiscus in the Caribbean as well as hardy and Rose of Sharon Hibiscuses here in Texas and they never complained. But yes, they can.
Good to know there are no pests. You will need to learn which pests are now common in Buffalo. Mealy buds for example, normally start showing up at the end of May and in June.
When pests eat the top, you can "see" with a lens that one part that is green has been eaten but the texture of the leaf feels normal if you pass your hand through the leaf. When it is PM, you can pass your fingers through the gray/white fungi and some of it sticks to your fingers.