What type of box is the VPN peer?
It could be an issue with PFS due to the presence of the Nonce, try disabling it on both sides and see if that helps as this can sometimes cause interoperability issues.
The next thing to check is the Proxy-ID/subnets (ID fields) and that they match between the two peers, some remote VPN peers are far more picky than others about what they will accept in that field.
Attend my online "Be your Own TAC: Part Deux" CheckMates event
March 27th with sessions for both the EMEA and Americas time zones