Chromadb only returns the first document from persistent db

### System Info

|software|Version|
|:---:|:---:|
|python|3.10.11|
|LangChain|0.0.209|
|Chroma|0.3.26|
|Windows|11|
|Ubuntu|22.06|

I have tried on both windows and ubuntu

### Who can help?

@eyurtsev

### Information

- [ ] The official example notebooks/scripts
- [X] My own modified scripts

### Related Components

- [ ] LLMs/Chat Models
- [ ] Embedding Models
- [ ] Prompts / Prompt Templates / Prompt Selectors
- [ ] Output Parsers
- [ ] Document Loaders
- [X] Vector Stores / Retrievers
- [ ] Memory
- [ ] Agents / Agent Executors
- [ ] Tools / Toolkits
- [ ] Chains
- [ ] Callbacks/Tracing
- [ ] Async

### Reproduction

i am having trouble adding multiple documents into a vectordb. I am using chromadb here.
The following loads, split and embed 2 text files and store them in a persistant vector database. Then it queries the database.

```python
from langchain.document_loaders import TextLoader
from langchain.vectorstores import Chroma
from langchain.text_splitter import CharacterTextSplitter
from langchain.embeddings.openai import OpenAIEmbeddings
import os
from getpass import getpass

OPENAI_API_KEY = getpass()

os.environ["OPENAI_API_KEY"] = OPENAI_API_KEY

embeddings = OpenAIEmbeddings()
text_splitter = CharacterTextSplitter(chunk_size=1000, chunk_overlap=0)
persist_directory = "db"
db = Chroma(persist_directory=persist_directory, embedding_function=embeddings)

# -------------------------- Adding spacex_wiki.txt -------------------------- #
loader = TextLoader("this_has_to_work/spacex_wiki.txt", encoding="utf8")
documents = loader.load()
docs = text_splitter.split_documents(documents)
db.add_documents(docs)

# ------------------------- Adding imploson_wiki.txt ------------------------- #
loader = TextLoader("this_has_to_work/implosion_wiki.txt", encoding="utf8")
documents = loader.load()
docs = text_splitter.split_documents(documents)
db.add_documents(docs)

db.persist()

# --------------------------- querying the vectordb -------------------------- #
db = None

db = Chroma(persist_directory=persist_directory, embedding_function=embeddings)

retriever = db.as_retriever(search_type="mmr")

query = "What is implosion?"
print(query)
print(retriever.get_relevant_documents(query)[0])
print("\n\n")

query = "Who is elon?"
print(query)
print(retriever.get_relevant_documents(query)[0])
print("\n\n")
```
The above code runs without a problem and is able to retreive from both text file. The problem starts with the following code.

The following code only loads the vectordb from the persistant location.
```python
from langchain.document_loaders import TextLoader
from langchain.vectorstores import Chroma
from langchain.text_splitter import CharacterTextSplitter
from langchain.embeddings.openai import OpenAIEmbeddings
import os
from getpass import getpass

OPENAI_API_KEY = getpass()

os.environ["OPENAI_API_KEY"] = OPENAI_API_KEY

embeddings = OpenAIEmbeddings()
text_splitter = CharacterTextSplitter(chunk_size=1000, chunk_overlap=0)
persist_directory = "db"
db = Chroma(persist_directory=persist_directory, embedding_function=embeddings)

# --------------------------- querying the vectordb -------------------------- #
retriever = db.as_retriever(search_type="mmr")

query = "What is implosion?"
print(query)
print(retriever.get_relevant_documents(query)[0])
print("\n\n")

query = "Who is elon?"
print(query)
print(retriever.get_relevant_documents(query)[0])
print("\n\n")
```
The above code will only return from the first document stored in the vectordb (spacex_wiki.txt), no matter what the prompt is.
The following are the text files used.

[implosion_wiki.txt](https://github.com/hwchase17/langchain/files/11850301/implosion_wiki.txt)
[spacex_wiki.txt](https://github.com/hwchase17/langchain/files/11850303/spacex_wiki.txt)




### Expected behavior

It is expected that information from both documents can be retreived when the vectordb is loaded from persistant location.
However, only the first embedded document can be retreived.