Good morning, this is sort of a version 2 of a problem we had a few months ago with the Android version of the Collector App: Found Here.
To sum it up simply, when we go to edit a point like a hydrant, one or a few fields with info already in them (all domains by the way) are cleared. In the example, "Open Direction" is cleared when entering an editing session. Sometimes things like "Ownership" are cleared also. The bug from a few months ago was app-breaking, luckily this one isn't.
I've replicated this on our Android tablets and on my Android phone, we had no problems on Apple Devices and in ArcGIS Online. The last bug was also Android only.