When I first purchased Audirvana 3.5 earlier this year (2021), I tried controlling it from my iPad using the Audirvana Remote app, but ran into various issues (I don’t even remember what they were exactly anymore.) This caused me to abandon use of Audirvana Remote.
A workaround that worked well for me and that I use to this day was to connect to my Windows PC running Audirvana via the Microsoft Remote Desktop Client app on my iPad. This gives me a virtual monitor of my Windows PC that I can view and interact with on my iPad. I then simply run the native PC version of Audirvana from this view.
Any type of remote access software should work for this. I chose Microsoft RDC because it is free. Microsoft RDC has been rock solid: always connects, no crashes. The advantage of this workaround is that you avoid any issues related to connectivity/syncing between the main Audirvana program and the Audirvana Remote app, and you avoid any issues related to the Audirvana Remote app itself (since you’re not running the Remote app at all.)
This really only works if you like controlling Audirvana playback from a tablet in landscape orientation. Also, some of the scrolling within the Audirvana main app is a little tricky, since you have to finger-tap on a very narrow scroll bar or screen region in some instances. (The “pointer” mode of Microsoft RDC can help with this, when you want fine control over where to click on the screen.)
Just posting this to the forum in case it helps anyone else.