One of the most difficult tasks in football is getting linebackers to have an effective pass drop.
Linebackers, by their nature, are not great pass defenders. When they drop in zone coverage they are normally dropping in the middle of the field and have to prepare for receivers coming at them from both sides.
The key to getting linebackers to be effective in their zone drops is to give them a limited responsibility and a clear set of rules they can use to be effective. Coaching linebacker drops is one of the most difficult tasks for a good linebacker coach.