two focal points KU band 5.6 m

Could be "saddle" distortion:  When the dish is tilted to point at a satellite the top and bottom distort forwards and the sides distort backwards. With the dish at its operational elevation, check using crossed tight strings, sideways and up/down across the front. Measure the gap.  The strings should just touch in the middle.

If that is the problem please say what rib / panel adjustment facilities you have.

Best regards, Eric

Here is how to adjust the sub-reflector https://www.satsig.net/sub-reflector-alignment.htm

But, this does assume that you can first get the dish in focus (feed to sub-reflector distance) with good nulls for both az and el simultaneously.

I've seen this problem (no nulls on one axis or the other) on a very "floppy" 4.5m dish. It is a real pain if you have a dish with no adjustments possible. 

Figure shows the height of the rib tips. Typically 12 measurements around the rim.  Should be all level. Actual heights, once dish is tilted to operational elevation, vary a few mm up and down, with the top and bottom coming up a bit, and sides going backwards.
It is not helped if the four sub reflector supports form an X. Putting stresses in the struts is then no use as the attachment points are all neutral, zero error points.

Cure is to adjust all ribs at the operating angle (very difficult to operate the theodolite and to make the adjustments) or return the dish to zenith and pre-adjust all the ribs the wrong way.

Do a crossed strings type test at the operational angle and then, with the dish vertical, make all the adjustments, gently, based on calculated estimates.  All assumes you have rib adjusters in the first place !!

Best regards, Eric