Special effort is required to receive weak signals with a negative Noise Margin.
Your tuner is stopping and moving on because the signals have a SNR below 15 dB.
Without a preamp, signals below NM -2 dB with an antenna gain of 12 dB can not be received because of the tuner NF that is added to the thermal noise floor and the minimum required SNR of 15 dB.
With a preamp, the antenna gain must bring the signal SNR up to at least the minimum required SNR plus the preamp NF BEFORE the preamp input, because the preamp NF makes the NM more negative.
Signals with a NM below -15 dB are buried below the thermal noise floor; antenna gain can not "pull them out of the noise."
Fortunately, the tvfool report has poor accuracy with 1 and 2Edge signals, and VHF signals can often diffract over terrain interference and the curvature of the earth to arrive at your antenna.