Birds move from place to place in search of food. Birds also migrate, so sudden changes at your feeder may simply be an indication that the birds have moved elsewhere to raise a family or headed south for the winter. Having said that, there are some very important things you can do to attract the birds in your area that normally come to feeders. Clean your feeders and keep fresh seed , suet and other foods available. Go look at your feeders.
Hummingbird nectar can go bad in a day or two in hot weather.
Offer protection for the birds. Plant Juniper bushes or Ivy or thick shrubs near the feeders so birds can dive to safety when Hawks approach. Offer a variety of food . Use a variety of feeders. Some birds such as doves eat on the ground.