Bob has been a cord cutter for nearly a decade. However, local TV is important to him and he's used an antenna for OTA signals for awhile. However, the FCC has sold off a lot of that spectrum, making it harder to pick up signals using his antenna. Leo says that FCC is also asking stations to move frequencies so they can sell off more of the spectrum. In most cases, all you need to do is run a re-scan on your TV to get the new station frequencies. You may need to do it several times. The FCC has a site that gives you the information here.
Mark's channels have disappeared from his Hauppauge tuner. What happened? Leo says that the FCC has made stations shift frequencies, and have advised that users rescan for missing channels. Check out TVAnswers.org for when and how to rescan. There's more information here - https://losangeles.cbslocal.com/video/4040289-cbs2-rescan-day/. But it may also be a Hauppauge issue.