RAM freezes and crashes my iMac after upgrade to iMac late 2015

Solution 1:

You could always take out the RAM and see if the problem still occurs. It could just be a coincidence that the problem started after the RAM was installed, in which case you've got another problem!

Solution 2:

Check that the two 4GB RAM SO-DIMMS specs match precisely to the two 8GB SO-DIMMS. Specs should be exactly the same except for the RAM capacity. The RAM you bought is definitely within spec.

Micron is very good RAM. Apple has used Micron RAM in the past. It's still possible you have some bad RAM and you would have to run the tests for many hours perhaps days to catch a failure when it happens. Definitely try taking out the two 8GB memory SO-DIMMS and see if the problem goes away after a few days of heavy use. Also try just the two 8GB SO-DIMMS by themselves. Then try an 8GB and a 4GB SO-DIMM and swap for the other pair. To trouble-shoot which RAM stick is bad.

Try putting the RAM SO-DIMMS in alternating slots. Many computers use alternate slots as channels. Slot 1 & 3 and Slot 2 & 4. It might make a difference when using different sized RAM SO-DIMM's. (Apple doesn't document this, it's just something many computers do with the slot channel arrangement) Apple might not actually do this, it's hard to tell. They list bank0/DIMM0, bank0/DIMM1, bank1/DIMM0, bank1/DIMM1 in the System Information -> Memory view. But it is worth a try to alternate the sizes.

4GB 8GB 4GB 8GB

Instead of

4GB 4GB 8GB 8GB

It will still run best with all four slots with the same sized SO-DIMMS.