Sounds like a lens coating or internal prism is failing, which would require
dismantling or replacement.
Bushnell will either repair yours, or send you a new model of similar specs.
Since the Banner was once the top scope, you'll probably get back a Banner
from a different manufacturing lot. If they can't do that, you might get an Elite,
which is a big upgrade.
I've dealt with them many times, since I live near and buy from their factory
outlet store, and am on a first name basis with the store manager.
A repaired, fully warranted banner like yours sells for about $80 as a refurb
in their outlet store.