This is actually not a bug or problem but misconfigured root tweak settings are causing the issue.
Issue: WHMSonic resellers see a blank white page when they enter to their WHMSonic panel on 2086/whm.
Reason: Under the root WHM >> Tweak Settings >> Security >> “Allow PHP to be run by resellers in WHM” option is disabled.
Solution: Login to WHM root >> Tweak Settings >> Security >> enable this option “Allow PHP to be run by resellers in WHM” then save the page.