What could cause one channel of RAM to fall off?

Question

Iron

Actually the essence: There is an Aourus B450 Pro motherboard, about a week ago a friend asked me to check the percentage for performance (Ryzen 7 2700), it was on my PC for several days, everything worked fine, then I put back my Ryzen 5 1400, PC I didn’t start the first time, the reason was most likely the dust that got into the socket, because after cleaning everything worked, but at some point I noticed that the system became bad and indeed, the task manager showed that out of 16GB the system uses only 8. From what I tried: I cleaned the legs of the processor and the socket with alcohol, dumped and sewed the BIOS, poked the dies in places (actually after that I realized that one channel was not working). In addition to everything, cpu-z and AIDA64 see all 4 dice and even show their SPD. The operative itself is 4 Patriot dies of 4GB each on Samsung chips (I don’t remember the exact model,

Answer 1

There is a suspicion that he injured his legs, which are responsible for the exchange with memory.

Answer 2

I had it.
Helped purge the slots from dust and reset the settings in the BIOS.
Moved several times to different slots

Answer 3

Get a magnifying glass... and check the pins on the socket. They have to be perfect... have the same angle and direction. If there are bent legs, then buy a needle in a pharmacy and "gently" correct them.