Why is the connection to the SQL, RDP and WEB server disconnected without a network connection failure?

Question

Computer networks

There is a "server" of the access control system (Win 7 x 64), the one with cards and turnstiles, and there are its clients. Microsoft SQL Server and the ACS server are installed on the server. Clients (Win 10) establish a connection to SQL Server by connecting as SA and to the ACS server using the REST-API. In addition, an adjuster sits at the client machine, who needs the server's desktop, which he receives via RDP, a standard utility. And now the essence of the problem: from time to time all three connections are simultaneously interrupted for various times, from 5 to 50 seconds, then restored. That is, the remote desktop is waiting to reconnect or reports that it can't connect, REST doesn't see any endpoint listening on the server, SQL just fails when it tries to act.
1. Working locally behind the server, the moment of failure for clients is not observed in any way. Network connection OK, desktop responding, SQL connection OK, IIS running
2. Crashes leave no trace in the logs
3. Network activity recorded by WireShark at the time of the crash is no different from activity when everything is normal, except that client connection packets are absent, and what is especially interesting there are no packets closing the session.
The bonus is the effect of presence, thanks to which I could not see a single failure and for three days I frankly thought that I was being deceived.
The network is flat, through several switches scattered across the floors. There are Cisco, TP-Link.
Has anyone seen something like this? I went through everything I know and can not find the reasons for this behavior. The installation is far from the first, but such a problem has never been seen before.

Answer 1

rings online?

Answer 2

The problem was somewhere within the server and remained unexplained. Solution: rebuilding the system from scratch, rebuilding the RAID, restoring the database from backup. It's a pity, it was an interesting problem