My Meridian PP came back to me saying that Meridian confirmed that the issue must be with my netwrok. So I have been playing a lot with the network set-up today and came to a conclusion that when I was trying to eliminate my switch glitching I have only tried Roon with a new switch and not Meridian Sooloos Config. This time I stripped the network and used my old 5 port NETGEAR switch, then re-typed the 818 and run the Sooloos Config and it worked! It has updated my 818 and it now works perfectly well with Roon and with my original network set-up.
The switch in question is TPLINK SG108, which looks and feels exactly as NETGEAR GS108, but will still be replaced tomorrow as I would surely not want to experience this outage again.
So beware this TPLINK switch if you have Meridian gear!
Thank you everybody for your support and valuable input!