I finally have everything working as it should but one thing i cant find on the forum and in the docs is how to tel one device in my network to use always use one gateway or interface, so not using the gateway group.
To attempt to state the above reply a bit more clearly.... create a new firewall rule, above the one that points to the gateway group, and specify your "one device" as the source and WAN2 as the gateway.You could also create another gateway group where WAN2 is a higher tier than WAN[1], and use that in your new rule - that way your "one device" would still have (some) internet access if ISP1 goes out of service for any reason.
I think you're making a mistake that seems to be quite common - in fact I'm thinking about logging an issue to suggest that OPNsense not allow it...When specifying a single host for a firewall rule, do not use a /24 subnet mask! Use the "Single host" option and the IP address with no subnet mask, or if you must specify a subnet mask, use /32 - otherwise your rule will apply to the entire subnet, not just the individual host.
I always use aliases for things like this - the alias GUI has separate options for Host(s) and Network(s). Unfortunately the rule GUI combines them as "Single host or Network", and seems to default to a /24 netmask, so it's rather encouraging the error. I'm still formulating an enhancement request