problems with AEC, does not respect the declared characteristics

[Nazar78]

Always connect the NAS directly to your ISP router else it will be doing double NAT. Also did you disabled the UPnP on this ISP router? Don't use UPnP and EZ Router. And have you manually added the required port forwarding to the ISP router? Any screenshot of the ISP router's port forwarding?

I don't know your ISP/location so I'm not sure if you can completely ditch your ISP router then replace it with the better capable Asus ac68U. This depends on your ISP's config if it supports 3rd party router on ONT directly or ONR in bridged mode. You'll need to find out or check with them.