Maybe a random glitch but I think I haven't seen this before:
Logged in with MS Edge and Firefox. Same result. I have rebooted the router at least twice after updating to 386.1_2 and router uptime was only 16 hours when I noticed the problem. Refreshing the browser didn't affect the situation. Had to reboot the router. After that the GUI was OK again.
What happens when you clear the browser cache or do a "shift-f5" (or ctrl-f5 in some browsers)?