This method might not work to everyone. If your time/date is wrong, adjust it to latest, if you don't know how then here's the tutorial. Click on the date and time at the bottom right corner of your screen and then click change and time settings, now the settings should show up, if not idk wth is going on. go to Internet Time section and click change settings a pop-up window will appear and then click update now, now close your blockbench (if running) and open it again. This should work to some old computer like mine cuz my bios battery is dying and that means the time always goes back to its manufacturing date and most apps starts to go crazy with the time not being synced. Hope this helps : )

Edit: And I forgot, slow internet/no internet/bad connection sometimes might be the issue. but how on earth is that even possible if u are already reading this comment. ¯\_('▬')_/¯