We have a number of external users who use one of our SharePoint sites to assign tasks to other users in our organisation. Each task is assigned using a people picker field on the form and this all works fine.
Recently we had some users leave the company and their accounts have been removed from Office 365 and also don't show in the SharePoint user profile service. If I (as an internal user) go into the form and search for these users in the people picker they don't appear. However, if one of our external users do the same they can still search for and select the old accounts in the form?
I'm not sure how this is happening. The last user profile sync ran last Friday afternoon and I can't search for these old users at all. I wondered if there's anything that would be preventing the external users from seeing changes made by the user profile service but I can't imagine that would be the case?
Any ideas would be welcomed as I'm at a bit of a loss as to how this is happening.