Just want to +2 this, on PC. Me and my friend both experience a sluggish UI. We've been playing around with settings to no avail.
We can see there's a separate process for UI which seems to take up a massive amount of processing time.
With other games built in the Unity engine, namely Rust and Starbound, there's been an issue where the text is being rendered using a ridiculously high number of polygons. Is it possible that this is affecting Offworld?