How do I fix this? problem in ipdate frames

I have problems with update frames…

Speed: 12

Mode Play:
PROBLEM → https://media.giphy.com/media/l0HUeMMfVv1SEM9IQ/giphy.gif
Mode frame per frame:
https://media.giphy.com/media/3ohc0WWRtds0f8pPyw/giphy.gif

Script: https://ghostbin.com/paste/fnq8k

What is happening?

My guess is that your ratio variable gets values greater that 1.
Try to use this:

ratio = Mathf.Clamp01(Mathf.Lerp(0, 1, t));