This is a common question.
Donation totals look at the transactions in a specific selected date range (as you would expect). However, fundraiser totals are slightly different. Fundraiser totals typically look at ALL the transactions for fundraisers that have a start date within the selected date range and therefore may include donations outside the date range.
For example, a fundraiser starting on the last date of the date range may have raised money from donations after this date that are included in the total. For this reason, the donation totals in GivePanel may differ from the fundraiser totals on the dashboard, fundraiser section, and in reports too.
Think of it this way...
Imagine you have a date range like 1st to 30th September.
Now imagine you have a fundraiser that started on 30th September.
The fundraiser raises €50 on 30th September and €50 on 1st October.
The Donation report for 1st to 30th September will show €50 as the donations totals are only looking at donations received between the date range selected.
The Fundraiser report for 1st to 30th September will show €100 as the fundraiser totals are looking at fundraisers with a start date that falls within the date range selected and then pulling in ALL income for these fundraisers, even if they received donations outside of the date range selected.