Q.hibiscus buds fall off
I bought a beautiful yellow hibiscus plant full of buds. I notice every day some buds fall off, they look like they’ve been cut. The plant is otherwise very healthy. The buds are “cut” on the stem just about a half inch below the flower bud. There is no sign of bug infestation but we do sometimes get ants and earwigs.
Thrips can cause the buds to drop early.
Even though your not seeing insects, you may want to treat your plant.
Neem Oil would be a good choice.
Here are some links.