Mailbox.org not working in regular window

Hello,

About a month ago, my mailbox.org email stopped being able to load on my regular Brave browser. The landing page is fine, but after I login the page never loads.

However, when I open a private Brave window, mailbox.org emails are able to load fine and I have no issues.

Please can you help with this? Any suggestions would be really appreciated

Kind regards
Lawrence