[bb88]

Likely you're in a blocked IP address range.

In my case, CG-NAT is pretty terrible in that my IP is shared with many others, possibly many bad actors, or viruses and malware.

[Aachen]

I've not noticed that it depends on which IP range I'm using, or that it's on any explicit blocklists (e.g. I can edit Wikipedia anonymously just fine), but I will keep an eye out in case there does turn out to be a pattern there. Thanks for the pointer