Issues connecting to the authentication servers

When I join a server, it often says "The authentication servers are currently not reachable". (1.png)

In Singleplayer, my skin is not loaded properly. It shows one of the default skins. (2.png)

When I join realms, it says "connection reset". (3.png)

If I connect to a VPN, the issues are solved, but that increases the latency and world loads very slow in multiplayer.

If I connect to mobile hotspot (China Mobile) instead of home Wi-Fi (China Unicom), I can connect to the authentication servers and my skin can be loaded properly. But still can't connect to Realms.

Is the authentication server blocked by my ISP?