Outside of re-flashing your SIMMS with a CD SuperBIOS/UltraBIOS cart & seeing if that clears it up, my guess is one of two:
One or more of your SIMM edges might be dirty & not making good contact. I would take the SIMMS out & clean the contacts on both sides of each of them with high-grade...
Yes that’s me. Or, supposed to be me.
I dumped this BIOS.
@Darksoft Can the 3rd attempt at my MAME credit *please* be spelled like my username here? :D
Just open it slowly from the fan side (put board upside down, then pull the two halves apart from the top of where the fan area would “rest” on the B board. Pry them open slowly (emphasis on slow!) which will increase your chances of separating them intact.