Probably bad bias offset. But the user has no control of that with ASIAIR.
If you are stuck with using ASIAIR, you might be able to use the dark frame subtraction in ASIAIR guiding...
In the Guide Settings window, navigate to "Guide Dark Library." Try to first select a gain that is at least close to the gain that you will be using. In the Guiding Dark Library settings, tap on autobuild. It will take perhaps two minutes or so. Then switch on "Use Dark Library."
This is not a cure-all, since you will lose some dynamic range.