Why don't services listening on port 1024 and above work?

Question

linux

There was a wireguard on the vps, listening to port 4443, everything was fine, then suddenly the tunnel fell, restarting the client and server did not help, I decided to put it on port 443, it worked, by trial and error I found out that services listening on port 1024 and above are not available from Internet, at the same time, such a problem is only with ipv4, everything is fine with ipv6, I started the services both from root and from a regular user - there is no sense. Iptables - cleaned all the rules, does not help either. What could be the problem, or is it the host's fault? I also noticed that names do not resolve if nameserver has an ipv4 address, if ipv6 - everything works.

Answer 1

I think the host...

Answer 2

What could be the problem, or is it the host's fault?

The hoster is not crazy to block all ports above 1024, and neither is the ISP.
The problem with accessing the server on the specified port from a specific device, or from all, incl. from mobile? If from one, then I would venture to suggest that perhaps some rule in the router is crookedly spelled out from which the connection is made. If from all, then somewhere the routing rules on the server are crookedly configured. See /etc/ufw/sysctl.conf and /etc/ufw/before.rules