Oh ok that’s interesting that yours results in different volume adjustments. I mainly stay in the WiiM iOS home app to control my sources. So either when I stream through the WiFi, tv through the hdmi, turntable through the line in or cd’s through the optical I notice the volume will go in increments of 3 using my phones side buttons. This happens in the WiiM home app. The only other app I use is the Apple TV app which goes in increments of 1 using my side buttons.
I hope that made sense and wasn’t too long winded lol thanks