After deep testing, we saw that if we reset the peer on the initiator side, strongswan does not reinitiate the connection by itself.
Need to add a connection initiation in the reset function on the initiator side.

I think the problem is similar to https://vyos.dev/T5611

After considering, we decided that reset is the same as terminate.
If you want to add a feature start manual initialization, please create a feature request.

In 1.4 and 1.5 command reset vpn ipsec has a termination meaning.

You can use the next type of configuration

set protocols bgp 4200010000 neighbor 2001:db8::2 address-family ipv6-unicast peer-group 'CUST_CR_IPV6'
set protocols bgp 4200010000 parameters default no-ipv4-unicast
set protocols bgp 4200010000 peer-group CUST_CR_IPV6 address-family ipv6-unicast
set protocols bgp 4200010000 peer-group CUST_CR_IPV6 remote-as '65500'

But we recommend to check the result in FRR configuration.

Rechecked - The issue exists.

I do not see this issue in 1.3.6