brittle forsythia branches
I treat my forsythia the same every year. I prune after it has flowered but this year it looks dead and the branches are very brittle.
Unfortunately sometimes you can't explain the loss of a healthy plant.
Forsythia are quite hardy, and my recommendation if you see no leafing out of the plant, would be to trim it down.
The roots may still be alive and then have the energy to start your plant growing again. I never give up on plants until I'm sure.
Here is link about forsythia care