I am pretty sure ISPs will not do any such things on their own, because there is no reason to play a moral crusader.

But I have similar problems in my place with other sites. my mobile internet fails with lots of sites for some reason and my fiber optic cant access renderotica without proxy from my IP and some time ago I had problems accessing same subnet IPs

My suspicion is that there are some errors in routing settings. Internet is pretty messy today and it is quite easy to screw up routes making certain ip adders ranges unreachable