I have added unicode arrows (and ellipses) to labels in my custom MixingStation layout. At some point in the past, they stopped showing up on the screen.
See, for example, my custom layout I put on github (currently line 17, search for "long").
The label just shows "long" on the application screen, when I edit the label in the layout-editor (push on label, choose "UI-Item" edit), the top left box "Layout / Label" also shows "long". When I click on the label, the popup-window for entering text correctly shows "arrow arrow long".
The .png file in the github-repository correctly shows how everything was displayed in the old versions (screenshot is from 2017).
Tablet is a SM-T520, running LineageOS 14.1-20180908-NIGHTLY-n2awifi, which is Android 7.1.2.
Mixer Model: XR18 (Demo Mode)
App Version: V1.2.0