I’ve seen this numerous times and was on the verge of tearing my hair out when I stumbled on “a” fix. Don’t know if it’s “the” fix:
On Win10, in Windows Security>Firewall and network protection, click on “Restore firewalls to default”
Once done, browsing proceeds normally. Suspect something gets altered in the firewall settings (by Brave???) that only triggers on some (unknown) event; apparently once triggered, it is persistent until the above procedure resets the firewall settings to default. Maybe. Perhaps. Possibly. Don’t have a clue what the trigger might be, but this may provide a clue.
Interesting facts: This behavior was never seen before installing Brave. Even then, I’ve never seen it triggered by another browser I still use periodically (Firefox). Additionally, once the “feature” is triggered, it also blocks traffic on other browsers I have installed (Edge, Firefox) until the block is cleared as above.
I never had the patience to refresh the page enough times to get rid of the error, so I found my “fix” instead. I don’t do anything to change configuration of the firewall settings, so I don’t expect the reset to have any adverse consequences. To date I’ve seen none.
Hope this helps! Good luck finding it.