So I've been investigating this issue today, and it's affecting both myself and clients.
Here's what I've found:
- The accounts that have been "broken" actually seem to be on a different platform of onedrive (best way I can describe it), maybe newer. You can tell by the share box which looks like this on "newer" platform:

As compared to the older style which looks like this on "older" platform:

- It seems that two OneDrive accounts that appear to be on different "platforms" are experiencing broken sharing and you can tell if they have different share boxes.
- Accounts where this sharing box matches each other, and therefore appear to be on the same "platform" can share folders without a problem. For instance, shares from my wife's account are showing up as links, and her account shows the "old" share box. However another account that was "broken" also has the same sharing box as I do, and I can infact share folders between the accounts properly.
- Creating a new account only solves this issue for a bit, because it seems the newly created account is created on the "old" platform and not the new one, but is randomly migrated at some point which breaks it again from sharing with the older style of account.
If you are having this issue, please check the shared from and shared to accounts, click on the share button for a folder, and see if the share boxes are different between the accounts. I only have limited accounts to test this from, so maybe more people can see if they are seeing the same thing as I am.