The local interface on the server sometimes becomes inaccessible. Why?

Question

linux

Good day to all.
There is a server on Debian. It is the gateway to the LAN behind it. It runs OpenVPN server, Resilio Sync synchronization server, dnsmasq DNS server, Transmission-daemon torrent rocker. The server has 2 network interfaces. One looks at the local network, the other looks at the Internet. Everything works well, but sometimes the ability to reach the server's local address disappears. At the same time, the server pings at its address from the OpenVPN network. Internet in the local network behind the server does not disappear.
I tried to look for tcpdump errors, but I did not find a solution. Also disabled on the server IPV6. Also to no avail. There are no errors in the server logs (/var/log/syslog). After some time there is no connection to the server address in the local network, it is restored by itself.
Tell me what could be the problem?