I got the Auto Tune feature to start working again by doing the following for the media client (STB):
Settings --> System --> Favorite Channels --> Flip by Favorites and then select "All Channels" (ie, instead of Favorites 1 or Favorites 2)
Note: Verizon support was useless for this problem. They ended up sending me a new STB which worked for a while (ie, until I went thru and manually selected the rest of my desired settings). Must be a recently introduced firmware bug (I'm seeing the same problem - and workaround fix - on multiple STBs).
Build Number, etc.: 24.18, 24.18, 24.12