Hub and Spoke (ADVPN+mode-cfg) not working after upgrading to 7.4.9

Hello,

used products: FortiGate 80F/FortiGate 400F

I have a simple Hub and Spoke Szenario, which works perfectly in 7.4.8 and less. If I upgrade my spoke to 7.4.9 I can't establish my VPN any more. 

Spoke says: 

ike V=root:0:vpn-pfi-hub: connection expiring due to mode-cfg client IPv4 error ike V=root:0:vpn-pfi-hub: going to be deleted ike V=root:0:vpn-pfi-hub: schedule auto-negotiate

Hub says:
twin connection 

Spoke config: mode-cfg, but with manual assigned ip on the interface
Hub config: mode-cfg, no ip assignment

There must have been a change in 7.4.9 - but I can't find it. If I downgrade, everything works.

Kind regards
TwoSoulz