Using a Mac, numbers in pivot table changing to text over time

This is my first post and I am hoping someone can assist me. I teach a financial modeling class at a University using a pc. Many of my students use Macs and most have no issues. One of my students, who uses a Mac, has an issue that I have never seen before.

When she correctly adds a formula to a pivot table , everything in the pivot table works for a short while. Then after 15 minutes or so, the formula calculations change to an error message.(I have timestamped screen shots from my student showing the pivot table with correct numbers at 3:14 and then the same pivot table with the error message at 3:36.)

What is happening is that one column of numbers in the pivot table (sum of annual amount) is being changed to labels. When I use the student's file on my computer, I cannot change the labels back to numbers, nor can I do other calculations with that column data.

Row Labels Sum of Attrition Amount Sum of Annual Amount Sum of Attrition Rate
Manufacturing 198700 856600 #DIV/0!
Technology 224600 1031100 #DIV/0!
Retail 133700 612300 #DIV/0!
Financial Services 195600 1101100 #DIV/0!
Durable Goods 29100 178600 #DIV/0!
Life Sciences 159400 739900 #DIV/0!
Grand Total 941100 4519600 #DIV/0!


Thank you

Rory - the source data is an excel file. Tks

Rory - I have requested the information about the software versions from the student.

The sample excel file is attached as well as a screen shot showing the initial correct calculation.

Thank you again.

Version of Mac software and excel are attached