Boolean Indexing on an object type

Hello,

How can I filter my dataset using standard pandas boolean indexing on an attribute that is detected as an object type ? (in the elastic mapping it is both indexed as "text" and "keyword"

Example:
``` python
df.dtypes
```
Results:
```
...
codeInstance object
...
dtype: object
```

``` python
df['codeInstance'].head()
```
Results:
```
YCzDDnkBdtlmoJ_PA5Qq instanceX
Name: codeInstance, dtype: object
```
``` python
df[df['codeInstance'] == 'instanceX'].head()
```
gives me 0 row.
I tried adding ".keyword" but it does not work either.