This sounds like a thermal stress kind of problem. The simplest would be what we call a cold solder joint. Here it could be the RAM chips or the flash chips within the SSD drive, next would be the CPU module either a bad heat sink or poor thermal bonding between the chip and heat sink due to old thermal paste.
It you have access to a hot air rework station you could try reheating the RAM chips using some good flux and fresh solder. If you have access to a spare SSD drive see if that works, and lastly carefully inspect the heat sink heat transfer tube for a hole. Look for staining on the tube and bottom plate where the tube sits. Then clean and reapply new thermal paste.