I am also having a problem with port forwarding rules. I had successfully added a couple of rules before. I just tried adding another rule and came across the same error. It seemed to be due to not having a unique name for my rule. I made the name uniqiue and clicked Save.
Is said the rule was saved, after a few seconds the continue button became active, clicked it, it took me back to the port forwarding page but my new rule was gone. No matter what I try, even though there are no errors, new rules do not get saved and keep disappearing.
Any solutions to this? Is this addressed in the new Beta? [which I am reluctant to try due to problems indicated on this board.]
I currently have 1.12