Maybe it's classic Matrox Mystique + Millennium II bus mastering issues that are causing the instability. I'd try a different videocard (or an integrated one if it exists) to troubleshoot whether or not the system is stable.

Can you reseat and clean every component in your system? Especially the contacts.
Is a memory test stable?

Garrett W wrote on 2023-04-30, 16:04:

Maybe it's classic Matrox Mystique + Millennium II bus mastering issues that are causing the instability. I'd try a different videocard (or an integrated one if it exists) to troubleshoot whether or not the system is stable.

Replaced the card with FireGL 1000. Red Keen and Jackrabbit freezing solved.

Threw in an Awe64 while at it, also appearing dodgy. At first, integrated card played sound only, and Awe MIDI only. After many IRQ changes, and internal card disabled, Awe handled both in 3D Bomber and Skyroads. Consequently, Jazzrabbit 1 quit playing sound at all. All setups would throw me out of the game, except Gravis setting completely freezing the system. Restoring IRQ to automatic didn't help either; just removed 3D Bomber's MIDI.

Idk. I suspect lack of IRQ's (POST once warned before disabling unnecessary stuff), or its 100W PSU is too weak.

PD2JK wrote on 2023-04-30, 16:04:

Can you reseat and clean every component in your system? Especially the contacts.
Is a memory test stable?

Could do that; not super tempted though due to lack of space.. :p

The lack of IRQs wont be a problem as long as the ones you are using are free?

I would certainly take some measurements of that PSU.