We had the same NO-PROPOSAL-CHOSEN error on the remote side of the Site to Site VPN.   We have found that with Load Balancing enabled and Active-Active AutoVPN set to Enabled, the Non-Meraki VPN peers can still only be established on whatever interface is set as the Primary uplink on the SD-WAN & Traffic shaping page.   We resolved the NO-PROPOSAL-CHOSEN error by using the correct Public IP of the MX on the remote side of the tunnel.   ... View more

This would be my advice too… or turn on ’adaptive’ - although I’ve seen this cause issues too but at least your Apple devices would still benefit.  ... View more