A dataflow that I had suddenly stopped work.
The error was
Encountered user gateway exception: '<ccon>ODBC: ERROR [HY000] Incorrect number of arguments: </ccon>
After a lot of troubleshooting, I figured out it was being caused by some steps I had added to add additional columns. Most likely, those steps were being query-folded to the database and it was not working.
I solved it by adding a call to Table.StopFolding right before I added the steps.
Table.StopFolding - Table Function | Power Query M