I doubt you can for the long term mix a core on an ancient 1.8 build and a remote on 2.0.
I know it worked in the morning, but maybe the remote updated? What is the precise version number of your remote, and is it Android or an iPad?
For the future, I would ask Antipodes why the Roon version on your K50 is so old.
Even the Room 1.8 Legacy version is now at build 1151, and there is a specific “Roon Remote (Legacy)” app version for that in the phone app stores, and a matching download for PC and Mac from Roon