Do telcos impose any restriction in terms of the websites allowed to be access on tethering connection? If so, where can I find more info about those restrictions?

I'm on Hotlink Fast prepaid plan (not unlimited plan), currently travel to Johor. Unable to access few popular text-based websites for research, work and Q&A:
- github.com
- stackoverflow.com
- reddit.com

Chrome is giving error ERR_ADDRESS_UNREACHABLE. Tried the following to no avail:
- use different browser: Safari, Firefox
- clear browser cache
- reset connection
- restart device.

NOTE: these websites are accessible if directly access from phone.

Interestingly, it allows access to video website like Youtube via tether

Some people reported similar issue for tether over Android, whenever Private DNS feature on Android is on. I've turned it off but no luck.

I suspect it's caused by telco end. I'm using Samsung phone and I can't even access samsung.com over tether, it would be interesting if their built-in security blocks access to their own website