This problem I am facing is in regards to the IM-425 SBC POS cash register machine made by Epson in the 90s, so this could be down to this specific machine's resource management, but could as well not be.

If anyone got any clues to this mystery I would be thankful:

Whenever I have a 16MB singlesided FPM stick in the machine, everything works as intended and both Win3.1 and Win95 accept the integrated F65545 with the standard driver package (for Win3.1 and Win95 respectively).
Whenever I have a 32MB double sided FPM stick (either parity or non-parity, both are supported according to the manual) installed, Windows 3.1 doesn't start until I change to a "non-linear" driver of the Chips and Tech package, and Windows 95 refuses to accept the driver from the W95 package at all and I have to fall back to ChipsTech "SVGA" or "Accellerator (new)", that are shipped with Win95.

Apart from that the system seems to run stable although, with 32MB inside, the graphics performance seems worse (when running the drivers I have to fall back to) as to compared to when using the 16MB stick with drivers from the official support disks.

The cash register supports up to 32MB either parity or non-parity, according to the manual. I set jumpers correctly (for 5V and double sided operation). What could be the reason as to the graphics card not working the exact way if I have the RAM maxed out in comparison to using 16MB only? Could it be a resource allocation thing that when using the full supported 32MB it has to make cuts somewhere else in the system?

What's interesting is the fact that the Win3.1 Chips and Tech driver works when I have the 16MB stick installed, but only works in non-linear mode when I have the 32MB stick installed.
With Windows 95 I have a similar issue, with the 32MB stick installed, only the "SVGA" or "Accelerated (new)" driver shipped with Windows 95 will work, and the one from the W95 driver disk won't, with the 16MB stick the driver from the disk works.

As well as the peculiar fact that most Win95 games won't run when using the 32MB stick, giving a "cannot start graphics mode"-error, which doesn't happen when running with 16MB RAM.
Even under DOS there is a similar issue, as apparently when running with 32MB installed, the custom VESA modes cannot be initialized (several games giving tantrums as to not being able to start graphics modes), but with 16MB RAM the graphics card works correctly. (Even the VESA test app fails when using the 32MB stick, and succeeds when using the 16MB stick)

I have tested multiple 32MB sticks, with and without parity, 3V and 5V, single and double-sided. But all 32MB sticks that are accepted by the system, will result in this - the graphics card acting/working in some "crippled" fashion, as to compared to running with 16MB.

Seeing as this is an Epson SBC it might have something to do with resource management?
PS, the SBC card only features one SIMM slot.

Any help would be appreciated.

PS: I have two SBC cards for this machine. A 486SX33 and a 486DX4-100 (which I am currently running)
And both boards support up two 32MB FPM parity/nonparity 3.3V/5V