OLE DB or ODBC error: Exception from HRESULT: 0x80040E4E

Here is a list that you can try:

1) Press Refresh All in Power Query Editor

2) Remove null values from your keys that you use connecting to other tables

3) Filter out errors from the table. Since Query Editor shows only 1000 line, the data error can be after that. By leaving in only error lines, you can debug this case.

4) Remove connections between tables

5) Rewrite merge commands: recreate merges you have with UI on the step just below them. Then delete them from the steps.

6) Comment out code until you succeed once, then return the code back
7) Simplify your M code: for example make merges by using SQL instead of doing it in M.