looking at the sniffer echo request reaches the firewall but did not leave it. Form my experience, 99% I had a similar issue it was either routing or firewall policy. I understand no routing is required as both vlans are directly connected. And from the other screenshot firewall policy looks good, too. But have you checked the logs on the Fortigate, anyway? Does the log is showing any denies? Are you sure the objects used in the policy have the correct IP configured? Because that has happened to me multiple time. Object name looks good but the IP configured in that object had an error like two digits in the wrong order or something.
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