Unable to use use "Concatenate or Join" function

[brian1]

I am unable to concatenate 2 tables. From the Tables view in the Data Manager tab I click on a table, then select "Concatenate of join" from the bottom of the page (three dots menu).  When I select the other table to concatenate, I don't see the menu for concatenating table, instead I just see the message "Select two tables to concatenate or join them". 

I did notice that there are some 500 errors: 

api/dataprepservice/v1/apps/abc-123-456/model/current/tables/transformations/recommendation?xrfkey=abc123

 The response error message is:

Unable to lookup the field! Dataset:abcd-1234-efgh, field:abcd-1234-efgh-5678

[Dalton_Ruer]

If you select a table and choose the "Concatenate or Join" option

You will then need to choose which action to take. I choose Concatenate

At the bottom of the screen I am prompted to "Select a second table...." 

I select my other table and then press Apply

The system shows tables that are concatenated with the overlaying circles above the table name

For added fun if you select a table(s) that are concatenated you can press the Split icon to un-concatenate them.