From my experience that error can be caused by something as simple as one column name being different to all the other tables you are querying that are the same structure.
The error messages like this in the query editor are quite poor I know.
To me it look as though maybe the 4th query (table) maybe has something slightly different. And then when the code attempts to move down to the next transformation there is some name that it can’t find.
I truly feel like this error will stem from a column name being slightly different.
On the code row where this is erroring out, how many column names are checked there. Can you go through these one by one and check they are referencing exactly the name when the query is in the previous state one before?