Myopenhab connecttion problems when using other networks

I have an odd problem connecting to Myopenhab with my phoneapp.
I know it worked in the past, but lately it does not.
I will first say when it works:
If at home and I change my ‘local openhab URL’ to a non existing one, the phoneapp changes to ‘connect to remote URL’ and I have access again, so I know my secret UUID and log in etc are all OK.

OK, so now I am away from home logged on to another network… phoneapp persists in trying to find the local URL and tells me there is no Sitemap file there.
OK, I change the settings so the local URL is something that probably isnt taken on that network, I see the app trying to connect to the remote URL, but there is always an error message of some sort, such as timeout or whatever, or cant resolve host.

Now ofcourse it could be that that one network has a problem, so I tried another one and onother one, and another one, all similar… but back home it works again.
Now some of those were public networks of the kind that do not require a paswoord, but you first have to go to their portal and accept the terms… which I did and which happily lets me access my mail and various webpages, but others were just regular private networks at friends homes
It just can’t be that my home network happens to be the only one in the vicinity that is configured properly.
Anyone any idea what is going on here? Is this even a true (My)OpenHab problem