When opening https://portal.manage.microsoft.com/

You see

You don't have any apps yet

Your company hasn’t made any apps available to you on this device.

Getting this device managed might let you access other company resources available to you, such as email and documents. Go to Devices to get started.

However when you open the Company portal app via the store if loads the apps list fine. This happens when you have multiple enrolled devices and the browser doesn’t know while one you have logged in with 

Solution

Click on Devices

Click on the grey bar

Click on your device you are using to access the Web and click Add