Crucial is well known for selling the most compatible memory for Dell machines.  Maybe you should give it a try. According the Crucial compatibility tool, the 3020 SFF can handle 16GB of DDR3L 1600 MHz memory.
I tried to upgrade my PC from 8 GB 1333 mHz RAM to 16 GB 1600 mHz RAM last year and it didnt work. I don't remember the blinking light code from last year and I don't have the RAM sticks anymore because I've returned them The RAM sticks were fine when they weren't paired with eachother (8 GB stick would work alone and so did the the other 8GB stick of RAM) The RAM slots were also fine. I am still wondering to this day what went wrong but my guess would be that my system couldnt handle 1600 mHz RAM.
I tried to upgrade my Optiplex 3020 SFF to 16 GB of RAM instead of 8 GB and it 
didnt work