I had an issue where movement would cause ram error and sometimes computer wouldn't boot it would just beep 3 times. I managed in isolate it to the bottom slot on 13" 2012 MBP. My computer was 10 years old so had accumulated a lot of dust and dirt over the years. I tried the spacers suggestion above without success so I tired the full overall approach. I completely dismantled MPB and removed the logic board so that I could clean it. I lot of dust and dirt had accumulated on the bottom side which compress air (e.g. from bike pump) cleared. I also noticed that there are lots long pins under a plastic cover for the bottom RAM slot (which connects into PCB behind the top ram slot) and there was lots of dust stuck between these. I carefully cleaning with plastic pointer and Electronic Cleaning Solvent.
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After re-assembling (ensuing keyboard ribbon cable with completely mated) the issues seem to have gone away.