+=>
-----
Trees and tree leaves that are moving because of wind will cause signal strength changes that can effect one channel more then other channels.
Moving trees also create moving multi path signals bouncing all around.
Wet trees and wet tree leaves make the situation worse.
----
Moving the antenna up or down can put the antenna in a better spot for reception.
A different location can improve reception.
Changing the antenna aim can help reception.
As a Test of reception , run a New continues length of coax from the antenna direct to 1Tv , no amplifier , no splitters.
--------------------
Also Digital Tuners can develop -Digital Glitches- that are not cleared out with simple channel scans.
To clear tuner do Double Rescan.
http://www.wchstv.com/DoubleReScanAlert.pdf