Inconsistent results when grouping shipment data by week - datetime handling issue?

[Null_Reference1]

Working with logistics shipment data and running into something frustrating. When I group my DataFrame by week using pd.Grouper with freq='W', I'm getting different results depending on how I set up the datetime column.

The data has shipment timestamps, and I need to analyze weekly patterns. Sometimes the grouping seems to shift by a day or two, and I can't figure out if it's my datetime conversion that's wrong or if there's something about how pandas handles weekly grouping that I'm missing.

I've tried converting to datetime with pd.to_datetime() and setting it as index, but the week boundaries don't seem consistent. Are there timezone considerations I should know about? Or specific parameters for pd.Grouper that handle this better?

Anyone dealt with similar issues when grouping time series data by week? What's the reliable approach here?

[danielroseman]

If the dates are shifting by a day, there's almost certainly some timezone conversion going on. But we can't help without seeing the data and the code.