Multi Wan setup from same ISP only one works some times.

[Gamester]

I have purchased a static IP from my ISP and as all of my devices are behind OPNsense firewall as in diagram below.

internet-->ISP router--(bridge)-->OPNsense router

I thought it would be good idea to connect opnsense to the ISP router as a client on DHCP on internal network as both networks (Static IP and Local broadband) are of 100mbps and could load balance them and kind off get speed of 200mbps (kind off)

Final diagram:


internet---->ISP router-----------------
                       | Local                      | Bridged
                       |                              |
                       ->Opnsense firewall<-

And also both do have different gateways.
For simplicity lets name interfaces as WAN1(Bridged) and WAN2 (Local)

So, the problem is that WAN2 only works some times so the connection drops and some computers suddenly have no internet and others have no problem.
If I enable only one WAN interface they work without a problem so there should be something else that needs to be configured and I have no idea what it is.

Also do I need to setup and firewall rules on either of WAN interfaces for the same?