Your host certificate is not RFC3280 compliant

Hello All,
I am on IPFire 2.27 (x86_64) - Core Update 160, three identical peers.
It looks like my VPNs connecting them are broken for some reasons, so I decided to get rid of the “Your host certificate is not RFC3280 compliant” warning, and do everything from scratch.
I deleted the certificates, but to my surprise, when I regenerated them, the warning was still there.
Also, the client package has errors when uploaded…
Googling the forum, I found many old post with the same issues, I’d expect they should have fixes already. I did not find an easy workaround (i.e. fit for my skill levels…), and I’m stuck in the mud…
Thanks for any advice,