Likely the antenna is failling.

What S/N values does it show in Service Mode?

A good antenna will deliver S/N values of 12 to 15, sometimes as high as 20.
I've seen bad antennas where the highest S/N value was about 3.

It is typical to have 3 or 4 satellites with S/N between 12 and 15, and the other satellites somewhere between 4 and 10.