Hi Anthony,
I’m using a Galaxy S8+ with Roon and SwiftKey and had the same extremely irritating problem.
The solution is to turn off “Full Screen” mode for Roon, leaving the Navigation Bar visible at the bottom of the screen. Irritating, but much better than not being able to type a search term.
You can do that by swiping up from the bottom of the screen and double tapping the small circle on the left of the Navigation Bar.
I’m not sure whether the disappearing keyboard problem lies with Samsung, SwiftKey, or Roon. I believe some apps have to be coded to properly handle the unusual aspect ratio of the Galaxy S8 series in full screen mode. It would certainly be great if the Roon guys can fix this in a future update.
Hope that helps,
Cameron