I have been using Mikrotik Routers for several years and have not experienced this issue yet.
I have an embedded device that uses a web page for configuration and uses the standard Port 80
Inside the LAN, I am able to enter the internal IP address and the login page appears.
I normally would use an alternate port outside on the WAN to access this webpage. IE: Port 81 on the WAN side maps to Port 80 on the inside
When I experienced the issue of the page not being accessed, I did a simple port forward Port 80 to Port 80 - it still could not be accessed.
I also tried different external Ports to be mapped back to the internal port 80 just for testing, still will not work.
I have several other devices that have port forwarding on this router and they work great. I have followed the same steps for this device and it will not work.
If this internal embedded device only has the correct IP address, but as an erroneous Gateway IP address, would that explain the device not connecting through the Router, but does connect on the LAN. Not sure if this is the case yet.
If this is the case, is there a work around to properly make this available on the WAN side, even temporarily.
The Mfg of the equipment needs to have direct access to this device for remote changes, after that happens, the port forward will be disabled.
Any other ideas?