[ADTech]

It is a mistake to think that all signals from a given origin will be homogenous at some other arbitrary point in space at some distance. It just doesn't work that way. Your antenna may be in a spot that is getting an odd-ball reflection that just happens to coincide with that channel's operating frequency.

Try moving the antenna and re-testing. It's a simple step and doesn't cost anything but some time and work. That will tell you if it's a signal path anomaly or some problem with the origin.

It's also possible that there's a kink or other fault in your cabling or splitter that's causing a "suck-out" at a particular frequency. You'd have to run a temporary coax to test that idea.

You may well need to do some detective work to find out if it's an issue with your receiving system or if it's on the other end. Good luck.