I don't know how to determine that.
On a side note, I found a backup of my system from a few months ago, and it had WSUS 10.7.3 on it with updates from Nov 2016. I used that to make a WSUS flash drive, and that one works just fine.
So something definitely changed in the WSUS version that is causing the issue. I guess it could be the updates themselves, not really sure how this works =P