I have set up a ProtonVPN IPsec tunnel recently by following their setup process. It seems to work fine, except for me getting the following error in logs: initiator can't find identity for peer: <name of peer>.

I have set up two peers, only one of which I am using as specified in the ipsec/identity and the other one in case I want to switch to at some point.
I can't seem to figure out why I am getting this error when the other peer is not specified anywhere else as being in use / initiated.

It's a question to the developers why an initiator peer that has no identity attached to it complains about that to the log periodically. Disabling such peer will stop the messages from appearing in the log.