Why are individual packets to the server lost?

Question

Asterisk

Welcome all.

There is the following situation: there is site-1 and site-2, united by means of a provider's VPN into one local network. Both sites have sip servers on asterisk, through which communication is established with each other.

After replacing two switches (provider and local) on site-1, the following problem appeared: the only trunk on this sip server that establishes communication with site-2 began to "fall off" periodically. This consists in the fact that this trunk in the asterisk logs turns out to be Unreachable, then back to Reachable. There are no breaks in communication.
There is also a self-written program that logs this sip server - it works through the com-port forwarded to it via TCP (port 2500). And periodically this TCP port turns out to be unreachable (from Wireshark- ICMP 74 Destination unreachable (Port unreachable)). Moreover, these are single "dumps" of the TCP port for a hundred successful responses.

Hanging up with the logger, apparently, eliminates the problem of the new provider switch (the logger and the sip server do not interact through the provider's VPN, only through the "local" router). If you need to configure something only in the "local" new router (this is HP 1920S) at site-1, then what exactly?