strongSwan

I am testing a new proprietary IKEv2 implementation for interworking compatibility with StrongSwan,
using v5.2.2 on Linux. Our implementation is able to reauthenticate the IKE-SA without drops
when interworking with itself, as described in RFC 7296 section 7.2.3, by negotiating a new IKE-SA
with new child, leaving the old IKE-SA in place, and when complete deleting the old IKE-SA and child.

I seem unable to configure StrongSwan to enable this seamless reauthentication, however. Am I missing
some configuration detail, or is this a shortcoming of the StrongSwan implementation (or possibly the
Linux kernel IPsec implementation)?

Using default configuration parameters, when StrongSwan decides to initiate reauthentication it first
closes the old SA. If instead the peer (our new implementation) decides to initiate reauthentcation,
StrongSwan again deletes the old SA before the new one is completely constructed, as a result of the
default uniqueids=yes setting. Changing to uniqueids=no however does not help, as although that
now leaves the old SA in place, the new SA's child fails to get created by StrongSwan as the kernel
rejects the IPsec policy, as it conflicts (is identical with) the old child policy.

I would be surprised if a standard StrongSwan VPN regularly drops the data connection, even momentarily,
when reauthentication is due (every 3 hours by default), so I'm hoping I am missing something obvious.