The performance improvement plan process is put in place with an employee to get continuing and consistent improvement.
If the employee is working at the right standard, it is best to keep working with the employee to support their development, without over-managing them. Make sure that you still have regular catch-ups and give regular positive and developmental feedback but agree with the employee to lengthen the time between catch-ups to let them develop their own work discipline and confidence.
If the performance drops again then restart the Performance Improvement Plan (PIP) for the areas that need focus. If the performance does not improve and it is within timeframe (eg 3 to 6 months) of the last warning, and it’s for the same or similar performance issue, then employers can rely on the warning rather than restarting from scratch.