Sheets Elapsed Time formatting not preserved on new rows

I have an arrayformula column that subtracts datetimes resulting in a duration. I format that result using Elapsed time custom formatting in Sheets:

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Problem is when new records are added, that nice formatting (h:mm) is not preserved. Resulting in decimal numbers like 0.377773. Not sure if this is a Glide or Sheets issue.

I know I can write a formula that’ll give me what I want but it would be quite messy compared to a simple [ End Time - Start Time ] formula.