Strong Signal, NO Picture, OTA

Hi, I'm new at this and forums. My 1939 brain is not the same as my 7 grandchildren's. They came into this world with a Ipod in one hand, me, behind a plow. I just went from my old tv to a new 70""smart tv", my wifes 54th wedding anniversary gift, and canceled my dtv account. Put up antenna, and pluged in my new Tivo Roamio OTA. Scanned for channels. Two of them have the same frequency and signal strength,(72%) but completely different programs. One of them comes in loud and clear, while the other one reads "No Signal". My question is, 1: Why can't they both come in loud and clear? 2: the signal strength is always 72%, never higher or lower, Why?