Dell has been building machines that are more picky about RAM since Haswell with DDR3L, so you need to stick to using quality RAM in anything newer than Ivy Bridge if you aren’t working with original modules (usually Samsung if factory installed). I usually recommend Crucial (Micron) or Kington in the Dells for aftermarket, as it seems to be accepted the best. They aren’t as picky as HP (will reject with a POST error if the timing is inconsistent on Elite and Z), but Dell has clamped down on the tolerances with the newer computers since you can’t get away with as much when the tolerances got as tight as they are on the voltages (1.3V for DDR3L, down to 1.2V for DDR4).
It sounds like you may have spilt something on the motherboard since you mentioned IPA - if you’ve already tried to repair it at the board level, then usually that means there’s serious damage somewhere that will not easily be repaired. Might be time for a new motherboard or laptop, since the boards can be quite expensive.
Look at it this way, especially on the RAM tolerances Dell has pushed on: I miss the days when you can get whatever is cheap on eBay as long as it works with 1.5V DDR3, but they had to do it because the voltage tolerance between DDR3 and DDR3L was reduced by .2V; DDR4 bumps that to .3V, so it was unavoidable. You can’t get away with accepting anything that’s in the slot when you went from 1.5V down to 1.2V! Even then, it was better to use good RAM but if you got it cheap and were okay with the very real risk of a no POST, it usually worked.