Clicking on Approve for a stage in Workflow isn't working

We have workflows setup and in the workflow we do have different stages (one per environment.) When the build is successful in one then upon manually approving the next stage, it builds and deploys to the approved stage.

Everything’s fine till yesterday but from today nothing is happening upon approving. There were no changes made in the accesses and permissions.

Can somebody tell what’s wrong or the fix for this?