The Douglas County portion of the ORION system has 7 simulcast sites that use LSM. If you try point the yagi at 111th and I St or 480/I80 Split you might have better luck.
What is happening your scanner is seeing more than one sites and the signal jumps up and down in strength. Then cause the drops out.
I have the same issue with the 996XT in the truck when in Bellevue. I also use the PSR500 and it handles the LSM simulcast better.
Here is the WIKI on what is happening.
Simulcast digital distortion - The RadioReference Wiki
Hope this helps.