It is an openHAB core problem unfortunately. The android app uses the official REST web interface and apparently one of the called endpoints is leaking memory. The android app might just call that very frequently so it happens more likely.
Next to REST it could also be the mDNS library that openHAB uses (which is bad code quality). Everytime a network peer asks for “openhab.local” the mDNS library kicks in and tells the local network about openHABs IP address. Maybe the android app does this quite often.
Someone would indeed need to investigate that sooner or later, otherwise openHAB cannot be deemed as being long-run-time stable anymore.
Cheers