Auto tune was a big problem back in the days of analogue,but at least you could see a poor station because of the noise or grain in the picture.
A TV aerial in theory receives only signals from the front but in practice its ability to reject side signals is not that good.
An auto tune as of yet isn't intelligent enough to select the strongest and best quality signals and use them.
So you may have bbc1 from transmitter A,good level quality and ITV from transmitter b coming from the side,which as poor quality values,leading you to suspect the aerial.
Manual tuning is an option but it can be quite tricky y to set up.
So what is the option,easy a filter that blocks out the signals from the weaker poorer transmitters allowing the auto tuning to put everything on screen from the correct transmitter,cheap and easy,if you some good channels and others poor give us a call we may be able to help.