Plex Plus -Tuner scan initially finds 44 channels (correct), but only list 20 at the end of the scan

I have a Hauppauge QuadHD tuner in my computer connected to a very nice HD antenna. I know that I can receive 44 channels, as the antenna feeds all the TVs in my house, plus I have the tuner connected to NextPVR in my computer, as well. When I run the Plex scan, it finds 44 channels at around 80 percent of the process, but when it gets to 100 percent, the number drops to 20, and excludes Fox, CBS, and CW. Should I just stop the scan at 80 percent, when 44 channels are showing, or is there a setting I need to adjust in Plex? Thanks.