Wow. That's quite strange, but thank you for your feedback. I don't have a very stable internet connection at home, so I tried to ping it from another vServer. The vServer is located in Canada, the server Simutrans is running on is located at Vienna, Austria (Europe), so don't wonder about the high ping of 141ms.
The result of the ping was impressively stable:
209 packets transmitted, 207 received, 0% packet loss, time 208241ms
rtt min/avg/max/mdev = 141.127/141.402/147.010/0.647 ms
So I guess this must be your connections fault. Maybe your ISP just having some overloading at moment and it will work fine in some days again.