I had the same problem - Hiding sheet worked in debug mode but not when running the script. Wickets answer put me onto what did work - putting the flush statement BEFORE the hidesheet atatement.

Script operation order:

• Activate DB_sheet

• Push data array to DB_sheet

• Activate User input sheet

• SpreadsheetApp.flush();

• SpreadsheetApp.getActive().getSheetByName(DB_sheet).hideSheet();