They said the problem is not repeatable on any other computer or device on the network except the M2 Mini. The problem also persists on the device in question between Safari (webkit engine) and Firefox (Gecko Engine), but sure, have them try in chrome (another webkit engine) to see if that "fixes it". If that doesn't work, reboot the router though the problem has already been isolated to this device. :shrug:
I'm not sure what is happening, but I would start by keeping the dev tools (F12 usually) in your browser open when attempting to replicate the issue so you can observe if any errors show up in the javascript console. You can also keep tabs on the "network" tab to see if any request are failing and if so they might give some insight as to what is happening.
Beyond that, I would say to try and search the web for "<router make/model> blank page after login" or things of that nature to see if there is anything specific to that router having issues.
Is the browser actually "freezing", as in "unresponsive" or is it just showing you a blank page? If the browser is physically freezing, it could be a hardware issue with your computer (bad memory? bad drive?), does this freezing issue occur in any other scenarios while using it? If it's just a blank page, there some browser security features failing or the browser is loosing track of the session cookie which is causing the web admin UI code to freak out and just show a blank page.
Its pretty hard to troubleshoot something like this without being in front of the computer (or on a remote session) and with limited information...
