DAX elapsed time calculation misbehaving?

Hello all!

 I have two seperate, but related questions on some strange results when I use DAX to calcualte elapsed business days from order palcement to order shipment. Both issues occur on both Desktop and Service. I am running the June Desktop update.

Please see the business case for further...

Business case: We are tracking how long a vendor takes to ship our products. One of our DBAs wrote a nice SQL/ M (I’m not sure which) query that gave us a raw calculation that shows time elapsed from order placement to the order being ready for shipment. However, the raw calc doesn’t take into account non-business days. I googled up the below DAX expression to at least filter out weekends. I couldn’t make the same thing for holidays. (Holidays aren’t the reason I’m writing, but if anyone has tips, I’d be happy to experiment…)

Column definitions:

order_initially_placed_at == I sent the order to the vendor for processing (date/time column)

order_received_in_hw == The vendor's system has acknowledged receiving the order (date/time column)

order_last_updated_at == Order has been assigned a tracking # and is awaiting pickup by the shipper (date/time column)

time_elapsed_since_order_placement == the raw elapsed time calculation (last_updated (-) initially placed) (text column)

business_days_elapsed == time elapsed rounded down to the day (whole number column)

Given this DAX calculation: 

business_days_elapsed = RoundDown (DateDiff (elapsed_time[order_received_in_hw], elapsed_time[order_last_updated_at], DAY) / 7, 0) * 5 + Mod (5 + Weekday (elapsed_time[order_last_updated_at]) - Weekday (elapsed_time[order_received_in_hw]), 5)

On the table “5 day question” (inside spoiler) why do some of the 5 day lags come out as “0” business days when the rest are correct? (This view is filtered to 5 day lag rows only) Aside from the other question below, the rest of the results are as accurate as they can be considering we’re rounding down to the full day.

A separate but related question: Using the same DAX calculation above, if one of the columns is “null”, why doesn’t the result always show as “0” on the report? The image below is a sample from the same table on Power Query. On the report (inside spoiler below the image), a couple do show “0”, but the rest… well, I have no idea where PBI is coming up with those results.

Correct null results showing in Power Query

Right now, I use conditional formatting on the column to make the text white so it is kinda hidden when the “last_updated_at” column is null. I’d love for the cells to be blank or “0” (or even “N/A”) when one of the columns in the calculation is null, but I’d settle for just understanding why PBI is behaving like this.

Any thoughts on either question would be appreciated!