There can be differing delivery metrics in the areas of your campaign reporting - below will explain some of these metrics.
Similar to how the impressions and clicks report have different delivery numbers in the data elements screen vs. the performance screen in Ui.Marketing, delivery numbers may also differ on various other tabs (browsers, geography, categories, etc.) when comparing these tabs with the performance screen.
In case you need a refresher for the data elements discrepancy: The performance report will show every impression that matches a data element. So if a user matches on three different data elements but is only served a single impression, the data elements report will show 3 impressions, one for each of the elements they matched with. That is why the totals do not add up or match the totals on the other tabs in these cases. Because of this, everything in the data elements tab should be taken as relative performance, not actual performance.
The Browser tab is slightly different, and this will show the internet browser determined to have been used upon the impression of an ad, however when we are looking at the browsers, operating systems, and the devices/OS settings, there will be some overlap because some of the browsers don't pull into the system. The main Web Browsers are Chrome, Firefox, Microsoft Edge, Opera, and Safari. There are three other Web Browsers (Pale Moon, SeaMonkey, Vivaldi) and some specific Mobile Browsers (like Samsung Internet, for example). Most of the time, the smaller browsers will fall into the "other" category. However, occasionally, we will see some runoff impressions that don't pull into that category for whatever reason. The impressions and clicks without a browser name registering in our system will cause these numbers to appear as less than the actual numbers, but you can always download the CSV file from the Browser page to see all the accurate numbers.
When in doubt, you should always look at the actual performance tab for the total amount of impressions and clicks because that will show every impression and click served and garnered. Whereas on some of the other tabs, there will be minor discrepancies.