MiniBatchKMeans returns fewer clusters than requested

### Describe the bug

For some samples and requested n_clusters MiniBatchKMeans does not return a proper clustering in terms of the number of clusters and consecutive labels.
The example given below shows, that when requesting 11 clusters the result only consists of 9 and requesting 12 results in 11 clusters. Requesting 13 clusters then yields only 10 clusters.
When using KMeans instead of MiniBatchKMeans there is no such issue.

### Steps/Code to Reproduce

```python
import numpy as np
from sklearn.cluster import MiniBatchKMeans

points = [
    [-2636.705, 892.6364, 239.4284], [-2676.219, 922.741, 227.3839], [-2628.628, 902.6482, 245.5609], [-2612.497, 860.9032, 248.924],
    [-2639.552, 993.8482, 211.2253], [-2602.453, 958.7801, 211.5786], [-2598.118, 1032.398, 177.4023], [-2582.155, 972.5088, 203.5048],
    [-2548.377, 803.9934, 279.4388], [-2550.095, 979.9586, 222.6467], [-2746.966, 1021.456, 188.8456], [-2745.181, 984.1931, 199.6674],
    [-2729.113, 973.8251, 201.8876], [-2720.765, 1014.262, 205.0213], [-2747.317, 1099.313, 146.2305], [-2739.32, 1005.173, 200.297]
]

for numClusters in range(7, 17):
    model = MiniBatchKMeans(n_clusters=numClusters, random_state=0)
    clusters = model.fit_predict(points)

    unique = np.unique(clusters)
    print("requested", str(numClusters).rjust(2), "clusters and result has", str(len(unique)).rjust(2), "clusters with labels", unique)
```

### Expected Results
```
requested  7 clusters and result has  7 clusters with labels [ 0  1  2  3  4  5  6]
requested  8 clusters and result has  8 clusters with labels [ 0  1  2  3  4  5  6  7]
requested  9 clusters and result has  9 clusters with labels [ 0  1  2  3  4  5  6  7  8]
requested 10 clusters and result has 10 clusters with labels [ 0  1  2  3  4  5  6  7  8  9]
requested 11 clusters and result has 11 clusters with labels [ 0  1  2  3  4  5  6  7  8  9 10]
requested 12 clusters and result has 12 clusters with labels [ 0  1  2  3  4  5  6  7  8  9 10 11]
requested 13 clusters and result has 13 clusters with labels [ 0  1  2  3  4  5  6  7  8  9 10 11 12]
requested 14 clusters and result has 14 clusters with labels [ 0  1  2  3  4  5  6  7  8  9 10 11 12 13]
requested 15 clusters and result has 15 clusters with labels [ 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14]
requested 16 clusters and result has 16 clusters with labels [ 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15]
```

### Actual Results
```
requested  7 clusters and result has  7 clusters with labels [ 0  1  2  3  4  5  6]
requested  8 clusters and result has  7 clusters with labels [ 0  1  3  4  5  6  7]
requested  9 clusters and result has  9 clusters with labels [ 0  1  2  3  4  5  6  7  8]
requested 10 clusters and result has 10 clusters with labels [ 0  1  2  3  4  5  6  7  8  9]
requested 11 clusters and result has  9 clusters with labels [ 0  1  2  3  5  6  7  8  9]
requested 12 clusters and result has 11 clusters with labels [ 1  2  3  4  5  6  7  8  9 10 11]
requested 13 clusters and result has 10 clusters with labels [ 0  2  4  5  6  7  9 10 11 12]
requested 14 clusters and result has 12 clusters with labels [ 1  2  3  4  5  6  7  8  9 10 11 12]
requested 15 clusters and result has 11 clusters with labels [ 0  1  3  4  6  7  8 10 11 12 14]
requested 16 clusters and result has 13 clusters with labels [ 0  1  3  4  5  6  7  9 10 11 12 13 15]
```

### Versions

```shell
System:
    python: 3.9.7 | packaged by conda-forge | (default, Sep 29 2021, 19:20:16) [MSC v.1916 64 bit (AMD64)]
executable: C:\Users\USER\.conda\envs\sklearn-env\python.exe
   machine: Windows-10-10.0.22000-SP0

Python dependencies:
          pip: 21.3.1
   setuptools: 58.5.3
      sklearn: 1.0.1
        numpy: 1.21.4
        scipy: 1.7.2
       Cython: None
       pandas: None
   matplotlib: 3.4.3
       joblib: 1.1.0
threadpoolctl: 3.0.0

Built with OpenMP: True
```

COMMENT:
In that case it looks like it would be worth adding it to the API documentation -- perhaps either as a note under `MiniBatchKMeans` or in description of `reassignment_ratio`.

Labels: Bug, module:cluster