I’m on 5.5.9(424) on Android. Maybe it already updated and you didn’t notice? or does the version on your app still show the old? (i.e. ignoring what play store is showing).
Honestly, sometimes this happened to me on iOS as well. For some reason, this app didn’t autoupdate. I had to go directly to the app on the App Store to see that there was an update available and click on it. I don’t know if it is the same on Android.
Very strange. My original thought was that maybe it’s related to different android versions (i.e. maybe older versions might not be compatible with certain changes or updates), but we are on same android version.