There are many reasons why you could be having trouble receiving a certain TV channel. The signal could be affected by different types of interference including but not limited to, communications signals, LTE/Cellular, Microwave feeds, weather conditions, physical obstructions or reflections etc.
If you are using a powered antenna or powered antenna preamp in your system, there is a symptom that is becoming common. Symptom, 'I can only record while the TV is turned on.' It's becoming quite common for preamps to operate on 5vdc, and the amp/preamp arrives with a USB power cable. You have a choice to connect the USB power cable to the provided USB wall power adaptor, (Like a cell phone charger) or, you can connect the USB power cable to a USB port on your TV. If you have it connected to the TV USB port, the amp will lose power when you turn the TV off.
In the scenario above, if you have programs setup to record, and your TV is off, your DVR may get poor or no TV signal. Your recording could be of poor quality or no recording at all.
Also, there could be times where the TV station transmission has been changed for some reason. The transmitter could be shut down while under repairs, or the station needed to temporarily reduce the transmit power. The Stations can make changes for up to 10 days without notifying the FCC. They can also reduce the transmit power to 80% of its normal output for up to 40 days without notifying the FCC. Temporary power reduction is more common with low power VHF channels. You can visit fcc.gov to further research this topic.
NOTE: These sites referenced below are not affiliated with Channel Master and we are not responsible for their content.
Signals and Reception
NOTE: 3 of the links below go to the HD Primer site. It is a valuable resource for easy to understand tutorials about receiving ATSC HD TV signals, and also addresses many common sources of interference that can degrade your signal quality. However, there have been some changes to the UHF band channel lists, that have not been updated on the site. Also, keep in mind that there are more communications signals present in our airways now than there were when some of his articles were written.
There have been two selloffs of UHF channel spectrum's. In the mid 2000's the FCC auctioned off the UHF frequencies above 700MHz. That left real UHF channel 51 as the new 'highest channel' that TV stations could use to transmit signals.
There has been another auction for the sale of the 600MHz through 700MHz UHF spectrum. Starting in 2018, TV stations that had used transmit channels 37 through 52, are required to transition to lower frequency transmit channels. The transitions must be complete by July 2020. By that point in time, the highest transmit channel will eventually be RF36. You may continue to see virtual channel numbers, higher than CH36. You can find out more details about how and when this might affect your stations on the FCC FAQ site.
The links below go to some very interesting and educational web pages, about ATSC HD TV. If you search the internet for information on this subject, you will find many thousands of 'search results'.
http://www.hdtvprimer.com/antennas/fixes.html
http://www.hdtvprimer.com/ANTENNAS/basics.html
http://www.hdtvprimer.com/ANTENNAS/ganging.html
Other good sources for technical info about possible causes for reception issues;
https://en.wikipedia.org/wiki/Tropospheric_propagation
https://otadtv.com/factors/index.html