Layer Missing from Mobile Map Package

[CiaranHiggins1]

Hi

I have been able to create Mobile Map Packages successfully using a Python script and via the GP tool except for one layer in the data. When I symbolize the polygon layer using single symbol it works fine. However when i use the unique value option on a certain column it does not appear in the mmpk.

The column I wish to symbolize on is called ACTION and is a text value 1 character long. This works fine in Pro but the layer does not appear in the mmpk. I have been able to get layer to symbolize using unique values based on the audit name but why is the action column which i need to symbolize on any different?

Thanks in advance!!