My Winegard amp has an inline power supply, in the coax. If my reception faulters, holding the power supply a certain way (seems as though if my hand is in contact with both ends of the coax) seems to correct the reception to near perfect. Lack of ground continuity?
Poor connection at either of the coax connectors, or the USB power port.
The center conductor or the shield connection at the coax ports could be bad.
I test the female coax connectors with a piece of 18 gauge (the same as the coax center conductor) bare solid copper wire to be sure it grabs it securely.