Same issue here on pixel slate tablet on pixel phone. Closing the app completely and retrying again is my go. It takes me a few tries. It needs to be closed also from background. If I just close it and reopen again without killing it from background, it never connects.
Sometimes it connects from the first time but for the most part, I have to try a few times.
From my windows laptop it works fine the times I have been using it, but it is uncomfortable to me using the laptop.
I just getting used to it. Lol. No issues with any other applications, just ROON remote app.
ARC works fine in my phone and in my cars with Android Auto. No issues after the initial setup. Oh well. I have NUCLEUS ONE as server. All connected it to my modem/router combo. No mesh network or any switch at all and I have this issues. Regards.