Thanks for joining the Community, @J A N
QuickBooks Online is a web-based application that uses cache and cookies to run faster, but sometimes these can also block web pages from loading or responding as expected. As a first step when experiencing such problems, we recommend clearing your browser's cache and Intuit-specific cookies to fix.
As a side note, Chrome is the recommended browser for QuickBooks, but you can also try switching between web browsers to troubleshoot. Hope this helps!