The portfolio on your App shows a live calculation of your return whereas your statement shows the return as at the statement date. In your first few months these numbers could vary quite significantly due to the short period that you have been invested.
For example, if you bought your asset in the past month, and have been fortunate enough to have already seen some income, you will see a percentage return on your statement. Then, if you then look two weeks later, the percentage return will have dropped on the App as it is being calculated over a longer period. Over time this will normalise and, within 6-12 months, the difference should be negligible.