Does this project only support certain CPUs under macOS?

I have a handful of machines. Some will easily pick up work units, others will not even if I suspend all other projects and repeatedly manually refresh. Also according to the server status page, there are TONS of WU's waiting to go and all servers are up, so it doesn't seem to be a system problem at all. All BOINC clients are the latest supported version on their OS.

Here let me make a list of machines, and whether or not they can get work, and maybe someone can find a pattern? Whether it's the CPU or something else I'm overlooking?

2012 Mac mini - macOS 10.15 Catalina - Core i7 - CAN get WUs

2012 Mac mini - macOS 10.14 Mojave - Core i5 - CAN get WUs

2014 Mac mini - macOS 12 Monterey - Core i5 - CAN get WUs

2018 Mac mini - macOS 13 Ventura - Core i5 - CAN get WUs

2009 iMac - macOS 10.13 High Sierra - Core2Duo - Can NOT get WUs

2009 Xserve - macOS 10.11 El Capitan - Xeon - Can NOT get WUs

2012 Mac Pro - macOS 10.13 High Sierra - Xeon - Can NOT get WUs

Ok the most obvious pattern is Mac mini / Not a Mac mini. But I really don't think that is it.
The other pattern could be the line between 10.13 and 10.14. But thats kind of an arbitrary divider, plus the intel Mac client is really old and says it runs on 10.5 and newer. You would expect the opposite to be true if that's the case, that the older the OS, the more likely it would be to work.

The most logical pattern I see is the CPU type. But the Core2Duo is very old and the Xeons are about the same age as the i5 so it seems weird that they wouldn't work, but the i5s and i7s do.

What do you think?

Another datapoint:

2009 iMac - 10.14 Mojave - Core2Duo - Can NOT get WUs