I'd try cleaning the DDR4 before sending off for RMA. May not accomplish anything, but probably worth a shot.
Electrical contacts on the DIMMs can be scrubbed with a Q-tip and isopropyl. "Electronics grade" isopropyl, anhydrous (>99.9%), not low-percentage drugstore stuff filled with perfumes and additives that'll leave (conductive) residues. Terpenes will work as well,
d-Limonene is an aggressive solvent which smells pretty (like oranges, mmmm!) and is safe on many *but not all* PCB plastics. A polymer-based electrical contact cleaner like DeoxIT or Stabilant-22 is even better and utterly guaranteed to be safe on all plastics. The trusty old "pink eraser" trick will scrub away grime very well, it can produce ESD harmful to sensitive devices (which have no real effect on unpowered RAM, though), but beware that it also erases thin layers of (relatively soft) gold plating off the contacts so it should be used only sparingly.
The DIMM sockets can be blasted with compressed air. Or scrubbed with a soft toothbrush. Or both. Isopropyl/etc might be used as well, although it (or even fumes from it) might harm the slot or motherboard component plastics (typically mere surface discolouration rather than serious bulk deformation, but still a risk better avoided). You could meticulously wipe each internal contact with a cleaner-coated wooden toothpick, but it's a tedious exercise in patience which can easily result in bent/damaged pins. You could try dislodging debris with paper edges, although toothbrush bristles tend to work better.
Chamois swabs are preferred over Q-tips and toothbrushes. Lint-free "electronics grade" not-Q-tips are also preferred, as are wooden "electronics grade" not-toothpicks. Even laboratory Kimwipes are preferred over common paper. But the good stuff tends to cost too much for just one little use and we all live in an imperfect world, lol, so just use the best stuff you have on hand which won't make more of a mess than you're trying to clean.
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