PowerBI Service changes year on refresh

I assume that is a explicit measure. If you right click on the field in the visuals field well you should be able to set the summarization off. 

I assume in your original data you only have a single value, which sums to it's value, when you have more data it grows. If this is not the case have a look at the underlying data to ensure you have rows per each person, and nothing is happening prior to the data getting into power BI