uPnP not working with OPNsense firewall

Hi everyone,
I am having trouble with YaCy and using uPnP with an OPNsense firewall on the latest version.
I could port forward 8090, but I was hoping to just use the uPnP function so I (and others) have to do less configuration.

In the config screen, I get the following message:
Configure your router for YaCy using UPnP:
warning Configuration was not successful. This may take a moment.

I have tried unticking it, waiting and ticking it again, and it makes no difference.
YaCy has been on for 44 days, it is using Java 1.8, and is v1.926.

uPnP is definitely working as I have other software using uPnP and these are listed in the uPnP status screen on the firewall.
What can I do to try and diagnose the problem?