@Carl thank you! I'll try that and let you know how it works! 

@Carl I tried doing that you instructed, but had no luck. It's still saying "connecting... trying to establish a remote access connection.". Am I doing something wrong here? In the Deco M4 app, I added two port forwarding HTTP. (1) for internal port 80, external port 9080. (2) for internal port 443, external port 9443. Then I set my WD Cloud to port 1: 9080, and port 2: 9443. Still no luck and cannot connect outside my home network :( 

I was facing the same problem with my Deco M9.

Followed the instruction and setup port forwarding for 9080 & 9443.

Since then when connecting from remotely (4G) it shows my folder structure but i cannot access any files when trying to open them.

@Jfringer I got this working and this is how i did it on my Deco vs WD Cloud

In WD Cloud set up HTTP and HTTPS

HTTP

External Port: 9080

Internal Port: 80

TLS

HTTPS

External Port: 9443
Internal Port: 443

TLS

within your Deco go to port forwarding and do the following

Name: WDCloud HTTP

External Port: 9080

Select the WD Cloud device from your IP list

Internal Port: 80

Type: TLS (it's set as ALL as default, change this to TLS)

Name: WDCloud HTTPS

External Port: 9443

Select the WD Cloud device from your IP list

Internal Port: 443

Type: TLS (it's set as ALL as default, change this to TLS)

Now the next point is vital, go to your WD CLOUD and restart the device. Once restarted you can now access the device outside of your home. To test I stuck my phone off the WIFI to use my mobile data and could now successfully connect where as my tests before I could not until I restarted the WD Cloud device.

I hope this helps who ever may be struggling