I'm having the same issue here, yesterday morning the page was visible, so I tried to register the number but got an error because the number was already registered, so I deleted the whatsapp account from the number, but when i got back to register again the page was blank. Today I tried creating another app and starting from scratch, but it didnt work either. The page with this issue is the wa-dev-console following: https://developers.facebook.com/apps/1200299004599082/whatsapp-business/wa-dev-console/?business_id=136878374742346