Cloudflare captcha pages when IPv6 is enabled

A couple of months ago I suddenly started getting Cloudflare captcha pages when visiting websites using IPv6, which kept happening with more and more websites as time passed by.

One website I regularly visit didn’t even show a captcha, just an access denied error with error code 1020 and a Cloudflare Ray ID with no way to get passed that.

After disabling IPv6 I stopped getting captcha pages immediately.

So I contacted Cloudflare support, they indicated that there have been multiple “security events” related to my IP-address(es), but they keep refusing to tell me what events exactly and that I would have to contact each website owner who is serving me captcha pages individually to get this solved.

Aren’t there any other ways of figuring out why this is happening?

Maybe related, although I doubt it: some geo-IP database has my /64 from Hurricane Electric (who offers IPv6-tunnels) registered in Germany, I’m not German and the tunnel-server I’m using isn’t in that country either… This particular problem causes Facebook to be a pain in the butt, it started translating part of my news feed into German and I’m getting Germany related notifications and suggestions.
I haven’t been able to find the culprit for that and since Facebook doesn’t have techsupport that’s willing to reply, I don’t know how to solve that one, without disabling IPv6.