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Just get a blank white page where you would normally enter your login credentials. Tried different browsers and clearing cache. cloud.sonicwall.com
I ran into this the other week while using Firefox. Using a Chromium-based browser seemed to resolve it. I haven't had to login since.
Gosh I dislike web developers favoring Chromium...
I have the same issue with Chrome-based browsers, but if you open Edge in an 'InPrivate' session it works fine.