One channel isn't tuning in properly
 

I have been using a ChannelMaster 2001 antenna for almost five years with great success. About two months ago one channel (KVLY-DT) began having tuning issues. The signal strength will go from almost 80% to zero and back again and it stutters cutting in and out. Most of the time is bounces between 70-80%. The 2001 is a pretty small antenna so I upgraded to a CM 2018 and it did increase the signal strength but it still cuts in and out. The transmitter for KRDK-TV is literally less than 2 miles from KVLY-DT and it has a solid 98% signal strength.

Signal report
The CM 2018 antenna is mounted on my chimney about 25ft above the ground and aimed directly at the KVLY tower.
The coaxial is about a 75ft run into the house where it runs into a 8-port distribution amplifier left over from when we paid for cable.
When I installed the new 2018 I used the existing transformer and coaxial.

Any help is greatly appreciated!

Fun fact: The KVLY and KRDK towers are the two tallest man-made structures in North America and third and fourth tallest in the world!

Interference, most probably multipath. Usually, it's due to tree growth or some type of new construction in or near the signal path.

Move the antenna and try again. Repeat as needed.

possible answer
 

Rather than multipath, I would suggest that your problem could be co-channel.
If there is another channel with the same transmitter frequency as the one you are trying to receive getting into your receiver, it could wipe out the channel you are trying to receive. In my case, I was receiving a UHF Channel 23 just fine one minute and the next, it faded out. How did I know this was happening? I did an update scan for channels and I was also receiving another couple of "far away" channels from the same geographic general area. The channel I was trying to receive is 66 miles away and the unwanted one was hundreds of miles away. This seems to be more common in the summer months when there is a lot of moisture in the air and a phenomena called ducting takes place. Signals can travel for hundreds of miles beyond where they are supposed to be received. Also, signal level did not change much.

Thanks for the reply. I tried this and appeared to have some success then … the same thing keeps happening.

I added terminators to all the unused outlets and I'm checking other cable issues too.

This definitely sounds like a plausible cause especially out here on the Great Plains where this isn't much geography to block distant signals.