@HanySyS I've got the same problem. It started after the latest firmware update today. I had 9 records forwarding to my server and can't add any more. I deleted 4 of them to see if there was a limit but I can't add anymore to that ip.  I cannot change the server ip without a lot of work to configure  the services.

  @jedihermit 

I figured the issue in this case, there was recrods of offline device with the same name as my device that i forward the ip for, What i have done:

1 - open deco app

2 - click on Online clients

3 - at the end of the online clients you will find offiline clients open it.

4 - I found offline device with the same name of my device

5 - Delete it

6 - forward the port now and it will work

This happend twice for me and i did these steps and worked for me every time.

  @HanySyS I solved mine today by resetting all three routers and resetting it up like new. Fortunately my devices all picked up on the same settings so I didn't have to reconfigure any of them.  I'm not sure I had the same problem since I've had that same ip reserved for about a year.