The issue could happen when there are some firewall/proxy network issues.
and also try to update your browser to the latest version.
Starting 06/02/2020, Microsoft Power BI will begin rolling out to all regions enforcement of the TLS 1.2 protocol for all encrypted connections. All modern web browsers (Edge, Firefox, Chrome, Safari and Internet Explorer 11) support TLS 1.2. Any customers having connection issues should ensure they are using the latest web browser of their choosing. Any client/server connections (such as API/Embedded calls, Mobile apps etc) also must support TLS 1.2 in order to maintain connection to the Power BI service. For more information, please refer here
If the issue still occurs, I would suggest you create a support ticket to get dedicated help.