I wonder if there are no updates or they are simply not pushed. Similar thing happened to Telegram [1]. Client is open-source and functional, but Google Play version is not what you can build from the source.
Explain Lavabit page phrases it like Magma supports only Trusted mode: "We envision Trustful mode as the mode of choice for businesses, which have regulatory requirements, data retention practices, and unique needs like escrow keys. Lavabit’s free and open source server, Magma, supports these users." Are other modes supported?
Code for DIME (Dark Internet Mail Environment):https://github.com/lavabit/libdime