Android: Highlight sometimes does not work

Basically the title, when I select some text to highlight, sometimes it works, but (for now) mostly it doesn't - nothing happens. Or maybe the text is highlighted but is not displayed as such.

System info (Newsblur is from F-Droid)

app version: 13.12.1 (256) android version: 13 (TKQ1.221013.002 test-keys) device: Xiaomi M2101K6G (sweet) username: SteveBuscemiDress server: default pending actions: pre:0 post:0 premium: yes prefetch: no notifications: no keep read: no thumbs: yes