Error 502 Bad gateway only on certain network

I tried clearing browser cache and cookies. I don’t have control over the server, I cannot restart it. I tried connecting with Tunnelbear VPN, and if I use the VPN, it loads over my home network too. If I plug my phone into the same PC that showed the error(with no VPN) and share my mobile data connection (with no VPN), it loads perfectly. I also have a subdomain https://ds.zambelly.hu/ that is linked to a different host than my main domain, and that one always shows the 502 Error with or without VPN, mobile data or home netork (altough I might actually have some problems with the host itself on that one).

Edit: I realised that I have a mail subdomain for all 3 domains. Those work on all connections. Now I am also pretty sure that the issue is with the host, but I don’t know what to do or what to ask for at my hosting service.

Edit #2: Now I have a theory: Maybe my host server ip-banned the local CF gateway? When I used TunnelBear’s VPN, I tunneled trough another country, which also means I used another CF gateway, and that solved the problem. I have contacted my hosting company and I am waiting for their reply.