Has anyone had any success in using the port triggering mechanism on a Draytek 2860 Router?

I am running a Vigor2860ac with Firmware 3.9.4_BT Build Date/Time Jan 10 2023 16:40:12

If I manually forward ports to a fixed internal IP all works as expected, but port forwarding should trigger this behaviour for any computer which send out the trigger enquiry through he right port.

The objective is to allowing incoming communications to different devices and laptops on an intermittent basis.

It works OK on a 2862, so I was wondering if this is a known problem or there some other factor I need to look for such as a Firewall Defence entry ?

Thanks

John N.