The problem is happening on any new images I upload with multiple partition, single disk - regardless of machine type. But at least I figured out what’s going on. So after I upload, I just have to copy the d1.mbr file from an older image and then the new one downloads okay. Thanks for helping.
Unfortunately I’m at the point in the year where I don’t have the time to troubleshoot further or update to newer trunks. I’ve made my images and next week we’ll begin deploying to around 3000 machines. I’m looking forward to new and exciting fog updates when I get to experiment more at the end of summer. Thanks for all everyone does!