Interrupted system call

Archer C20v5 with openvpn keeps disconnecting randomly, between 5 and 15 minutes.

Wed May 31 06:39:31 2023 daemon.err openvpn(C20)[1615]: event_wait : Interrupted system call (code=4)
Wed May 31 06:39:31 2023 daemon.notice openvpn(C20)[1615]: SIGTERM received, sending exit notification to peer

What could be the cause of this?
RAM use is around 51% and 22% cached, some 600 KiB disk space left.