Why are incoming ip connections not going through?

Question

Computer networks

2 weeks ago the problem began - periodically stop passing incoming connections to the router.
We have three points on the satellite Internet, there are microtics behind the satellite modem. Mikrotiks have changed at two points during this time. Thus, we have the same glitch on 5 different Mikrotiks. At three different points. The glitch started around the same time. The glitch goes away after rebooting the modem and (rarely) after rebooting the Mikrotik. In the second case, I suspect a coincidence, because once at a time it doesn’t happen. All these two weeks I've been hammering two providers.
What it looks like:
Internet works on points, sip via satellite works, no problem, I can connect to servers via ammyy admin, but! RDP does not work, I cannot connect to the router's admin panel, that is, neither forwarding works, nor the router does not respond. Ping at this time goes. Still it turned out to be connected by a telnet, at the very beginning, then I did not check. SSH hangs, hangs, falls off by timeout. Winbox - mikrotik configuration utility - can hang for a very, very long time. RDP similarly hangs, establishes a connection. Forwarding ip-cameras to the admin panel does not work in the same way, the browser very quickly gives out that the page cannot be displayed.
I've never experienced this and don't know what it could be. The provider hasn't helped either.
I ask you, tell me what it could be and in which direction to dig?
Satellite communication - two-way. Location - taiga in Khakassia, there is no other connection. Ports are open, I scanned Nmap, I telnetted there. It seems that there are no response packets.

Answer 1

So, if you have a satellite, is it just a satellite (two-way) or do you have a classic economy scheme with two providers?
Further, the problem can be in several places (in order):
1. On the network \ on the computer from which you are checking the connection (and further down the list in this section) (check - take another provider, for example, a USB modem)
2. At the provider satellite Internet ports are closed (check - transfer the publication to the 80th, it is unlikely to be closed and check)
3. There is an error in the firmware / settings on the modem itself (check the settings)
4. An error in the Mikrotik configuration (check the settings)
5. An error in the configuration Drop rules (disable)
Well, it would be nice to have more scheme \ less description of symptoms =)

Answer 2

Internet works on points, sip via satellite works, no problems, I can connect to servers via ammyy admin, but! RDP does not work, I cannot connect to the router's admin panel, that is, neither forwarding works, nor the router does not respond. Ping at this time goes. Still it turned out to be connected by a telnet, at the very beginning, then I did not check. SSH hangs, hangs, falls off by timeout. Winbox - mikrotik configuration utility - can hang for a very, very long time. RDP similarly hangs, establishes a connection. Forwarding ip-cameras to the admin panel does not work in the same way, the browser very quickly gives out that the page cannot be displayed.

I'm assuming the problem occurs when using at least some of the protocols that run over TCP. There is an assumption that the provider is probably somehow differentiating TCP traffic from UDP. This may be due to the use of "internet accelerators" a la Transport Flow Optimization in Cisco WAAS.

in which direction to dig?

Make sure that TCP and UDP behave differently (I'm not sure which protocol ammyy admin is using). If possible, wrap part of the "problem" traffic in VPN-over-UDP. Observe the situation. Study TCP behavior between points of interest. You say you have access via ammyy admin to the servers. If I were you, I would raise a tcp service on one of the servers (by configuring NAT ("port forwarding") accordingly), periodically access it from the client, saving traffic dumps at both ends. In my view, this can be automated. If the hypothesis is confirmed, and a difference is found in the dumps, you can ask the representatives of the provider a substantive question with this data.