1: debug flow basic will give you all the details, why it's getting blocked.
2: In your logs there some Source NAT when it's working and there is no nat when it's not, not sure if this is relevant.
3: can you check the policy id and the route from the firewall's CLI : as below :
get policy from <source zone> to <destination zone> src-ip <source-ip> dst-ip <destination ip>
get policy id 18
get policy id 3
get route ip <ip which is not working>
get route ip <ip which is working>
Thanks,
Vikas