Hello Peter,

I am also using the Avalon M-Zero OBS mount with the following configuration:

William Optics GTF81 OTA
ZWO ASI1600MM Pro main camera with EFW
ZWO ASI290MM (guide cam) on OAG
ODroid N2 running Ubuntu Mate
Pegasus Astro Pocket Power Box Advanced
Avalon M-Zero OBS mount USB connected (from INDI mount general info, M-Zero firmware is Avalon - 62.0 - 11062019 )

I never encountered a situation like yours and even though I need to refine my polar alignment, the targets I shoot have always been within the field of view of the ASI1600 sensor. On that regard, I do not quite understand what may be wrong. One thing that may be different is that I do not use the Avalon hand controller and, as such, it is not connected to my mount.  You may try to use the mount without the hand controller to see if that solves this problem. 

Concerning the guiding, I successfully use the following parameters (see included screenshot):

Exposure: 1 second
Bin: 1x1
Box: 64
Guiding Rate: 0.500 (P: 133.33)

Let me know if any of this helps.