I’m not sure how this percentage figure is calculated. It differs from my spreadsheet, which is (number of shares * price * exchange rate) / (total buying cost-total selling income)
It’s approximately the same give or take FX fees, but if you sell part of your shares and buy more later, the figure becomes wildly different, so I guess it’s pairing up oldest buy with most recent sell or something.
But I’m using the spreadsheet for all my decisions anyway. I only refer to the values in the app occasionally to verify the number of shares is correct (i.e. I’ve not made a mistake somewhere) and the value is approximately correct.