When an IPsec peer is defined in the usual way (i.e. using defaults, or not being “passive” in manual config) it frantically starts to establish the session. When unsuccessful, because the peer is offline, an error message is logged once a minute.
Please consider implementing some way to limit that trying, or at least the logging. E.g. when the session cannot be established, increase the timer and/or refrain from logging, or limit the logging to e.g. once an hour.
It could also be useful to have some option to “ping first, if no reply then do not establish IPsec”. Of course that would have to be optional because replying to ping cannot be an absolute requirement to be able to establish IPsec.