Hi @SIMMN,
It creates multiple internal rules within the LINA engine for NAT configuration referencing a Security Zone / Interface Group with multiple interfaces, one for each interface. I'm not sure on your topology or desired outcome but it could be worth considering the option to leave out the Destination Interface object and use 'any' which will let the routing table decide, as opposed to explicitly setting the destination interface.
It was discussed in this reddit thread previously, however, it is not a bug.
https://www.reddit.com/r/Cisco/comments/qpnpo3/fmcftd_destination_nat_with_security_zones/
Please see the following excerpts from the FTD Configuration Guides. Doesn't matter which version, it's been like this for some time and still is even in the latest releases.
If more than one interface in an interface object exists on a given device, identical rules are created for each interface. This can become an issue for static NAT rules that include destination translation. Because NAT rules are applied based on first hit rule, only the rule created for the first interface configured for the object matches traffic. When configuring static NAT with destination translation, use interface objects that include at most one interface per device assigned to the NAT policy to ensure you are getting the desired results.
When sending packets, the device uses the destination interface if you specify one, or a routing table lookup if you do not, to determine the egress interface. For identity NAT, you have the option to use a route lookup even if you specify a destination interface.
Hope that helps somewhat
