Cisco ASA FortiGate 100F VPN Intermittent Connection

Hi, I have a Site 2 site VPN between our office, one end we have ASA and the other is a FortiGate 100F 

and 6 subnet each on both end of the firewall, the traffic between has been intermittent, sometimes it works and sometimes it doesnt. but the VPN shows its up

Below is the phase2 config on the Fortinet

config vpn ipsec phase2-interface
edit "XXXX"
set phase1name "XXXX"
set proposal aes256-sha1
set dhgrp 14
set replay disable
set src-addr-type name
set dst-addr-type name
set keylifeseconds 3600
set src-name "XXX-VPN-Group"
set dst-name "XXX-VPN-Group"
next
end

config firewall addrgrp
edit "XXX-VPN-Group"
set uuid XXXXX-XXXX-XXXX-XXXXXXXXX
set member "XXX.XXX.X.X/XX" "LOCAL-SUBNET-XXX.XXX.X.X/XX" "LOCAL-SUBNET-XXX.XXX.X.X/XX" "LOCAL-SUBNET-XXX.XXX.X.X/XX" "LOCAL-SUBNET-XXX.XXX.X.X/XX" "LOCAL-SUBNET-XXX.XXX.X.X/XX"
next
end

config firewall addrgrp
edit "XXX-VPN-Group"
set uuid XXXXX-XXXX-XXXX-XXXXXXXXX
set member "XXX.XXX.X.X/XX" "XXX.XXX.X.X/XX" "XXX.XXX.X.X/XX" "XXX.XXX.X.X/XX" "XXX.XXX.X.X/XX" "XXX.XXX.X.X/XX"
next

Any help is greatly appriciated

Regards