Policy Based Routing works for few seconds then packetloss ensues

[netflow]

I have a basic opnsense setup with 1 LAN and 2 WANs (2 gateways). No special firewall rules or routing or wan load balancing or HA - just default routing - if WAN1 goes down hopefully it'll goto WAN2 because of priority.
 
When I create a FW rule on the LAN (IN?) for a SOURCE host IP (I added it to a group) that goes to DEST ANY to go out WAN2, click apply then it works for a few seconds. I can run speedtest and ip check from that host IP. All good. Then a few seconds later I get about 50% packetloss and it's very spotty from there.

Q: Is there anything special I need to do to have an IP use WAN2 other than select its IP or GROUP in the SOURCE and DEST ANY then choose the GW?

Q: Is it just as simple as adding 1 firewall rule on the LAN IN side?

Q: NOTE: Since WAN2 is also natt'd, do I need to turn off NAT going out of that gateway? Seems like Opnsense automatically nats everything so turning that off doesn't seem simple in the nat setup as I'd be forced to use manual NAT mode right?

Q: Is LAN IN the correct direction to use for the rule for Policy Based Routing from a device on the lan to goto wan2?

Thanks!