The “suspects” in question are docs.google.com and gmail.com, fairly common URL’s. Unfortunately, they appear to not be working with any shields setting. For gmail.com:
and then:
I believe that Google may have made an update intentionally or unintentionally that causes erroneous redirects or data processing issues (my guess, anyway). Please make an update as soon as possible. 
Thanks!
Hi
Disable Brave shield.
This solution was proposed somewhere else for the 400_ERROR
plz, if this works let me know.
Hi Plasmi
I tried all other suggestions i.e. shields/cookies etc. All failed. I love Brave Browser but was logging in to Opera (which I hate!) to access gmail. Just by chance I right clicked on the Brave icon on my home screen (PC) and then “Troubleshoot Compatibility”. It ran a check and found issues (it opted for Windows 8). I clicked on Fix Issues and saved. HALLELUIAH - IT WORKED!!! Has been working perfectly ever since. Good luck - it is worth a try.
For future reference; and, the fix that you found, is also listed in the following:
This topic was automatically closed 60 days after the last reply. New replies are no longer allowed.
