Pulling straws here, but I'm wondering if it has something to do with the Direct TV splitter?
As far as VHF goes, I find VHF inside the attic to suffer quite a bit compared to UHF's with fringe signals like yours. I am using an attic mounted 91XG & YA-1713 feeding 3 sets with a 3414. The main Baltimore UHF's are good 24/7, but 11 & 13 are unwatchable, except very late at night until 10:00 in the morning. Otherwise, I am seeing all the way down to
WBFF-45 after trying every possible location in the attic.