User with project position has lost security access to one of his/her projects, but remains ok on others

If you have a user with the same project position on multiple projects, however security permissions seem to be different from one project to other, there are a few key areas to check:

1. Check the project position securities and ensure that the user has the security permission ticked still. 

2. Ensure the project position securities is the same for the workflows linked to the project types in question. For example, you may have one workflow linked to one of the projects and a different workflow linked to another. You may also have the same position created multiple times foe different workflows if the permissions are not the same. 

3. Check the workflow > object > Security for project positions. Again they may have been configured from the workflow level. Project position securities can differ between the two if they are configured in that way. 

4. Check the project sign offs - if there is a sign off sent for approval (from the current or future phases) then the user will not be able to edit until the sign off authority has actioned the sign off. In order to open this back up, the sign off authority will need to resubmit the sign off.