DPD on a standalone Firepower

[hilotbo1]

Hi all,

Apologies if this has been mentioned before but losing the will to live with a strange issue.

Have a S2S VPN between an FTD and a PFsense box that keeps dropping. I think it's something to do with DPD but can't for the life of me find anything relating to it on the Firepower... have looked for both DPD and NAT Keepalive, am I missing something glaringly obvious?

[MHM Cisco World]

vpn topolgy> advanced > IKE 
or 
vpn topology > advanced > IPsec 

vpn topology > advanced > tunnel 

MHM

[ccieexpert]

Please run debugs that will provide more details on the failure:

https://video.cisco.com/detail/videos/latest-videos/video/6365082403112?autoStart=true