By web-ui are you talking about the page that asks you for your password? Is it possible to hit the stop button on your browser to stop the page from refreshing? If so, log in and hit the stop button in your browser again to stop the dashboard from refreshing and click settings/update from file and upload the same firmware you are on now to the MBL. With any luck it will go through and fix your OS. I have uploaded the same os version I am on now in this manner and it worked without issue MANY times.
There have been a lot of changes made to the last few firmwares
GIT installs without a hitch on my spare 02.11.09-053 box with no abnormalities
Anyways, without RMA’ing the box or cracking the case open (which will void your warranty) and debricking from a linux live cd, the dashboard trick above is the only possibility I see for you to get your OS back in working order again.
An RMA or cracking the case open would be your last resort