Adding index nullifies other columns

 I have a really bizarre problem. I'm importing data from Microsoft Dynamics 365 into Power BI with the Cds connector.

My steps are:

1  Source

2  Navigation

3  Remove columns

4  Add index

And then some columns' values all become null. There is no filtering or joining before these steps

What I've tried:

-The data type is automatically recognized as Text. But just in case - adding a step to manually change it to Text still has no effect