A reinstall is definitely not necessary, but it’s also not harmful.
The webui is basically just a bunch of NodeJS scripts that live in /usr/games/minecraft. More than likely though–since the webui and the scripts haven’t been updated in some time–is that your NodeJS version changed (updated) from the system end.
Take a look at /var/log/mineos.log and see if there are any stand-out errors.
Then take a look at this post and a few of the entries below it to see if the webui running. Megathread for MineOS webui issues
Feel free to share any of the logs you see, as it will assist in the troubleshooting.