You can try updating/resetting the web ui with the following commands:
Sudo into root:
sudo -i
Then running the following commands:
cd /usr/games/minecraft
git fetch
git reset --hard origin/master
rm -rf node_modules
npm install
chmod +x mineos_console.js
Then after rebooting, it should work.
Also, check /var/log/mineos.log (you can upload it to a site like pastebin and link to it here)