Dataflow refresh fail due to "Error: Value cannot be null." error

Hello, 

This error first started between 530 pm MST on May 13th and 630 am MST May 14th. All of my dataflows (Data gateway connected to offsite SQL server) started failing, scheduled and refreshed. 

The error I am getting is "Error: Value cannot be null." and ";Parameter name: plainText Request ID: 34d209d5-d223-474b-9bc9-988a4e3ba0b1 Activity ID: 17508a4f-e111-4feb-b29c-8a8b681f7ea1". 

Not sure where this null value is (source or setting in the table of the data flow) . Our PowerBi developers are struggling to figure it out to so I figured I'd reach out here for help.

Thank you