VIA needs drivers for correct initialisation (4in1 etc)
the 128MB stick is possibly an one-sided module, which aren't accepted well by all boards.
Basically the highest address bit is undefined, might cause glitches. Better use a correctly-recognized module.
I am not sure whether DOS 6.22 can handle >8GB, too lazy to search the web.

If the board only see's 64Mb of 128Mb ram stick there is an issue you need to correct before going further. I suggest you try a 2GB partition (as what Win95 orig and FAT16 supported) and see what happens.

The RAM is absolutely something that will be fixed, but I'm out of 64MB sticks at the moment. I bought more from that place with all the old hardware -- just waiting for it to show up now.

I'm pretty sure it's not the lack of VIA drivers, as there's no 4-in-1 driver package for DOS 7.1. 😉 Nor is the 2GB partition, or for that matter the 10GB disk, an issue with OSR2.1 -- that I know from prior success. The BIOS appears to be OK with it, as I tried a 20GB disk and it properly detected that as well.

I have some new data, though ...

I tried swapping the primary and secondary channels (CD on primary, HDD on secondary). That actually worked long enough to get a complete format. However, it took a long while to copy the 88MB of Win95 setup files to the HDD. (It's only a 6x CD-ROM, but still...) Setup ran, but it seemed to get stuck periodically. When it finished installing, and started creating program groups and all that, Windows processes would randomly crash until the whole thing just bombed. Not good.

I decided to fiddle around in the BIOS, and make a bunch of changes to see if I can change the behavior. I turned off L2/L3 cache, anything that mentioned burst or pipeline or turbo with regard to PCI timing. I also noticed that, whether running the CPU at 2x66MHz or 2x75MHz, the PCI Clock was still 33MHz. I then noticed the ISA clock was PCIclk/5, so I turned that down to PCIclk/4 (33.33 / 4 = 8.33MHz).

I then swapped the drives back to their normal positions. (HDD on primary, CD on secondary.) Format worked fine, the files copied in the amount of time you would expect, and setup ran without issues. Windows was able to boot successfully, Plus! installed OK, and it ran for an hour at the desktop without catching fire.

So far so good! Now I just have to turn on all the go-fast features until something breaks again. (But I'm leaving ISA at 8MHz.)