I'm not sure where to start because on the one hand, you're pretty far up the food chain on this stuff, Marv, so anything I suggest you have probably already tried. On the other hand, I know that sometimes we get tunnel vision and just need a fresh set of eyes. If the browser error you were getting was one that basically said, your current security settings put your computer at risk, there is a registry fix for that, but it sounds like you're past that and now dealing with Satan Incarnate 10.
Yes, out of sync clock can cause that error, and sometimes if setting it to the correct time doesn't work, oddly enough, you can go back in time and set it to a previous time and it will work.
More commonly, I believe that error points to a TLS issue. I think it happens when TLS 1.0 is disabled, but don't quote me on that.
We also lock our Sonicwalls down pretty tight, so often I will see something like this when our Geo-IP blocking is getting in the way because it's trying to hit a server in India or some other restricted place.
Resetting the TCP Stack may be needed along the way. Also I suppose you could activate by phone, but I would rather do a packet capture then talk to Pakistan.
BTW, it sounds like you have all the necessary corporate editions, etc., but if not, let me know.
The one thing that doesn't make sense, is why were you having issues with two different versions? I don't believe in coincidences. What at the hardware level could be doing this? I hate to use the U word, but have you updated BIOS and/or run the Intel Driver & Support Assistant?
Added:
I just found what I was looking for on the TLS:
https://docs.microsoft.com/en-US/troubleshoot/windows-client/windows-7-eos-faq/troubleshoot-extended-security-updates-issues