Why can l2tp tear neatly after 1 minute of operation?

Question

Network administration

Good afternoon. There is an l2tp connection with authorization and a secret key. The bottom line is: after connecting to the server, exactly a minute passes and the connection breaks (pings stop going), after about 5 minutes, Windows (seven) finds that the connection is broken and offers to call back. Tried on two l2tp servers - the result is the same. Another laptop in the same network clings without problems (so the problem is not in the provider and not in the router). Those. someone breaks the connection on the computer itself. Help identify it.
What has already been done:
1) Antivirus: regular avast, never had any problems with it and disabling it did not help. Disabled firewall didn't make any difference either.
2) The connection always breaks - I'm downloading something, or I'm just pinging a server. Exactly a minute (+ - a couple of seconds) - the ping does not go to the server.
3) netsh winsock reset; Resetting TCP / IP settings via AVZ did not help. The scan of the AVZ system did not produce anything useful (Files scanned: 801, extracted from archives: 0, malware found 0, suspicions - 0). The driver for the network did not update - the latest version is on the mother's manufacturer's website.
4) sfc /scannow said that all files are normal.
Dear gurus, tell me how you can diagnose this problem and identify the cause of the break.