I think this medium post has a detailed explanation of what could be the cause of your problem, I hope this helps. https://medium.com/@kerberjg/resolving-issues-with-ikev2-vpn-in-apple-devices-fb6d5795e587 Thanks for sharing this post; in my case setting PFS Group for the proposal to `modp2048` fix...

Setting PFS Group for the proposal to `modp2048` fixed the issue – apparently, iOS/macOS tries to renew the keys requiring this PFS Group. Previous value I had was `modp1024`.