Why does one resource not work through PPTP?

Question

firewall

Guys, help, tell me.
Faced with an ambiguous situation for me:
1. There is a Linux VPS. It has a PPTPD server. Masquerading and routing also work.
2. There is a Windows machine that connects to PPTPD, and the Internet also works, it roams the Internet, but the browser says about a timeout on a site such as sfs.gov.ua. All other sites are running.
3. If you telnet for example this sfs.gov.ua:80 from the vps where pptp is installed, there is a response, but not with windows.
4. Tracing showed that packet transmission is torn somewhere in the middle of the path.
What could it be?

Answer 1

https://www.opennet.ru/docs/RUS/LARTC/x2657.html
I suspect that this is the problem. And the site that doesn't work is actually not one, others just haven't noticed yet ;)

Answer 2

where along the way? behind your pptpd or between pptp clients and your public interface gateway on the server?

Answer 3

The problem is most likely with the TCP segment (i.e. MSS)