Disclaimer : I do not use ARC and have no need for ARC
Since you will be at home for Xmas (?) try using Roon NOT ARC.
While a part of the Roon Eco System you are evaluating ARC not Roon.
Take some time to read the forum and you will see that what you are seeing is not uncommon, ARC is a relatively new addition to the Roon portfolio and to be honest has not exactly shone for all the reasons you are outlining. You will also note that most of the fixes in Release notes refer to ARC , which with the best will in the world is work in progress !!
The inclusion of cellular, 3/4/5 G connectivity etc is adding variables into your evaluation that Roon has little or no control over eg stabillty of cell coverage over large areas
ARC is a extra to Roon, so condemning Roon because ARC doesn’t work is a bit like criticizing your Mini’s engine because the car radio doesn’t work !! 
I’ll start a thread “my 10th year with Roon” , and tell a completely opposite story of an infinitely stable server / transport system working on ethernet in my home using 2 completely different server protocols (Windows 10 and ROCK). In 9 years I have never experienced a connectivity issue or any other technical issue
Just a thought