EDIT: Issue ended up being Hardware Acceleration on the Draytek being enabled for IPSEC. Disabled this and VPN works without issue.

LAN to LAN VPN between Draytek and Meraki is up, routes showing on both sides, however no connectivity. Can't ping the routers from either end, no errors showing in the logs.
We had a Draytek 2866 at this site, replaced with a 2865 due to other issues. VPN was connecting fine on the 2866. Config setup from scratch, was preconfigured and sent to site.
Running the latest available firmware, 4.4.1_BT. I know in 4.4.0 there were changes to the VPN, and they added WAN > LocalHost, whether these changes are having an effect. None of the other sites are on 4.4.1_BT.
We've had a similar issue when replacing Draytek's for their other sites, however in those instances the VPN was working in one direction (From Draytek to Meraki, but not from Meraki to Draytek. This ended up being a Draytek firewall issue.)
Tested adding additional filter rules (WAN > LocalHost etc.) and disabling the data filter all together (Default rule set to pass), however issue persists.
VPN is using IKEv1 (Couldn't get it to work with IKEv2), and tested various security settings, as well as resetting up the VPN on both sides a few times.
Tested both Dial In and Dial Out.

Any further ideas? Is this a known issue with the latest firmware?