More likely you could have pushed or pull too hard on the CPU while change the cooler - it happens
- was the used AIO "hard to remove"?
- did you do it with a warm CPU?
- did you use a twisting action?
- did the CPU stay in the socket?
- Did you keep the cooler level while removing & installing coolers?
- did you check the socket, if you had even the slightest issue - after removing the AIO?
OK, now that I cover some basics above & Because you say BIOS2 work just fine
Test: set RAM to the Mfg voltage as stated on the side of the RAM .... sometimes BIOS sets it too low
CPU voltages - double check they are the same as before ? can the air cooler really keep it cool enough?
I avoid XMP & set timing manually, has proven to be more stable too many time to bother counting