Here's pause and adjust an employee's vesting schedule when they go on a leave of absence.
You can stop a security's vesting during a leave of absence.
In the Plans & Equity Awards tab, select the grant. Then, select "Exercise & Termination":
Stop vesting for employee as of stop vesting date:
When the employee returns, you can select "Restart Vesting". Vesting will be resumed from the when it was stopped.