Hi Charlot, unfortunately it's impossible to achieve a restoration rate of 100% on live pages, because Texmarker has to indirectly find the correct text passages after reload. The most common reasons for a failure are the page's content having changed since your last visit or the a script is rendering content after the page has fully loaded. For the latter you can just try the retry button in Textmarker's sidebar.
The only way to assure a reliable restoration of your highlights is to save the corresponding page - i.e. locally or using a service such as Pocket - and combine it with activating saving for immutable pages under Settings > History.