Task updates and approvals not working on some projects

I have come across a complex situation in updating the project using Project Online Tasks and Approvals options. On some old projects that I was managing using MS Project Desktop when I try to update the tasks by allowing team members to send update to PMs and PMs approving it. What is happening is that team members send the status updates, it goes to the PMs for approval, however when PMs approve them the status is not reflected in the schedule, meaning schedule does not get updated %progress.
Have you ever come across that situation? Is there any solution to that problem?
Kind Regards
Owais