How to properly use blendshapes via script? (c#)

Hello, I need advice on how to script blendshape animations. What I try to do is, making a 25000 polygon female model blink with her eyes, in random intervals. The blendshapes are all showing up correctly on the mesh. I put the following script on it, but when I start the game view, the eyes are closing in big steps with no transition until they are almost completely shut and then unity crashes with the "unity editor stopped working"-message. I use this script, will try to comment my idea:

     using UnityEngine;
     using System.Collections;
     
     public class BlinkControl : MonoBehaviour {
     
         SkinnedMeshRenderer skinnedMeshRenderer;
         float blink = 0.0f;
         float blendSpeed = 1.0f;
         bool eyesClosed = false;
     
         void Awake()
         {
             skinnedMeshRenderer = GetComponent<SkinnedMeshRenderer>();
         }
     
         void Start()
         {
             StartCoroutine(Blink());
         }
     
         private IEnumerator Blink()
         {
             if(!eyesClosed && blink < 100.0f) //as long as the weight < 100 and eyes are open...
             {
                 blendSpeed = 20.0f;
                 skinnedMeshRenderer.SetBlendShapeWeight(46, blink);
                 blink += blendSpeed; //...increase weight
             }
             else eyesClosed = true;
     
             if(eyesClosed) //if eyes are closed...
             {
                 blendSpeed = 10.0f;
                 skinnedMeshRenderer.SetBlendShapeWeight(46, blink);
                 blink -= blendSpeed; //...decrease weight
             }
             else
             {
                 eyesClosed = false; //set eyesClosed to false to restart the cycle... 
                 yield return new WaitForSeconds(Random.Range(1.0f,8.0f)); //...as soon as 1-8 seconds have passed
     
             }
             StartCoroutine("Blink"); //restart coroutine
         }
     }

I don't know what the problem is. Any idea?