How does the Model Open Analysis Report change without any changes to model?

We've come into performance issues on our model and requested a Model Open Analysis (MOA) report from Anaplan support. This was very helpful in identifying modules and, in particular, line items that were using up a lot of processing power. The metric they used was Total Calculation Time, measured in milliseconds.

After we made a number of formula enhancements, we requested an updated MOA to measure the improvements in the model. We noticed the total calculation time on line items we didn't touch, changed. Some increased by quite a lot.

We then purposely didn't make any model changes and asked for a 3rd MOA and noticed there were a lot of changes in total calculation time despite no new inputs, formula changes, etc.

Has anyone else experienced this? Is there an explanation on why it would change? Or is it not a correct metric to use?