[Update 2020-04-20] My Synology has been responding slowly during FCPX edits, so I decided to revisit the RAM that I purchased. It turns out that one of the two 16GB sticks must be bad because I tried the 16+4 stick setup as mentioned earlier, and it wouldn’t boot. I tried the other 16GB stick and it booted quickly. Annoying. The problem was a bad stick all along.
Below is the original post from 18 Dec 2019.
I recently bought two sticks of Crucial 16GB DDR4-2400 SODIMM 1.2V CL17 non-ECC RAM (CT16G4SFD824A) hoping that I could upgrade my Synology DS1819+ from 4GB to 32GB. Unfortunately, when both sticks of the RAM are installed, the NAS doesn’t boot, and instead simply blinks the power light indefinitely (even after waiting 45min).
I did find that when I installed one 16GB stick alongside the existing 4GB stick, the system would boot, recognize the stick and report 20GB of RAM, but it also gave the warning about non-Synology RAM. I’m guessing this is because the RAM I purchased was non-ECC, whereas the Synology RAM is ECC.
For now, I’m returning to my 4GB configuration.