error when sharing list

Hi all, MS support was not helpful, so hope you can support me in how to fix.

My wife and I we are using private @outlook.com accounts. We are heavy users of todo and we have some shared lists between our accounts. So far all good, all fine.

Now if i create a new list, no matter if in browser, ios app, .... i have to switch to another list and to switch back to see the share button. If i click it, there is the error that a problem has occured and link can't get created. Please try again. If i do so, it works and a link is created.

If my wife then tries to open such link, she gets the question if she wants to access list XYZ like it should be and it always was. If she does it, there is an error "the list was not found, please contact the person who shared with you.

We have the exact behaviour if she tries to share with me. The exisitng, already shared lists, are running well.

Any idea or thoughts, how to overcome this issue? 
Greetings, Dennis