A little update to this issue.
I finally had enough of it so bought a Ryzen 3600, X570 Asus motherboard and some new RAM which was running perfectly for a week. I then played about with RAM timings and messed a few things up. This issue started appeared now and again so was considering re-doing the cabling. I returned the RAM OC to default settings and it disappeared for about a week.
Yesterday, I used the DRAM calculator and bumped my ram from 3200CL16 to 3600CL14. System appeared to be happy but then this issue came back and would drop the connection the same as before but more frequently.
This got me thinking back to my previous machine and it more than likely ties-in with changing from 2-dimms to 4-dimms late last year!!
I'll be reverting my RAM OC this afternoon but I am confident it will go back to working as normal.