One user complained that his project gets locked (shows by himself) many times within one session.
Actions: He checked out the project in MSP added hours against a tak and uploaded back to clarity it got uploaded without any message. Updates can be seen in clarity.
The project is still shown locked.
He hits unlock does some work goes to gantt, verifies dates and returns to properties, the project is locked again.
Resolution: This was one off situation I guess then gantt was locking the project(yes, it did that) as I could see a warning on top saying the schedule is modified and "Save or Discard" needed.
As soon as the gantt was saved without any changes, the lock disappeared completely.
It is to be expected that a project would be locked if you make any changes in the Gantt and not save them.
See this thread for some more discussion ; Project everytime got locked when accessed Tasks by Gantt