Not sure if this is the right place for this, but let's see.
I have a client who has just moved from Wunderlist, one of his colleagues sent him an invite to join a new list. So far so good, he gets the invite, clicks it, then get's greeted with "You are not a member of this organization blah blah blah". He opens it on his Android phone instead, boom, straight in! Log back in to the web client on the PC, and it's there in all it's glory.
If that didn't confuse me enough we then installed the Windows 10 App from the store, he can't even log in with that one, constantly returns error "80090016".
I'm at my wits end with this one, please put me out of my misery.
@axeblokie We're having a similar issue. Our links for shared lists don't allow us to log in with our organisation's accounts on Windows, but if we use the same links on a mobile device, we can add the shared lists correctly. The probably has only started recently. Even the links that we'd generated in the past and used for multiple users are now not letting us log in with our organisation's accounts. I haven't found any solution or workaround on Windows yet unfortunately.