transparent mode 600E not Working

Hi

I have a 600E running FortiOS 7.4.3 in transparent mode.

There are 10 VLAN subinterfaces on the server-farm side and one VLAN subinterface on the outside for the servers’ gateway.
All interfaces are in the same forwarding domain.

Client requests coming from the client side work fine.
However, servers located in different VLANs (but in the same forwarding domain) cannot ping each other and also cannot ping the gateway.

I have a policy that permits any interface to any interface, all sources to all destinations, and all services.

When I replace the 600E with a 70G or 100F, everything works correctly.

Does anyone have any idea what could be causing this?