Sometimes you keep getting the message “Initializing, please wait a moment” for hours. This can happen if you moved the sim from an Android phone to an Iphone and used whatsapp on the iphone for few days. Now after moving the sim back to the old android this Initializing message wont complete and whatsapp gets stuck. I contacted Whatsapp support and they asked to uninstall and reinstall whatsapp. After reinstalling whatsapp and entering phone number on the whatsapp screen, it prompts to ask if you want to restore from a backup. Click yes as this is the only time you can get back your old whatsapp messages and data. After that it asks for google account and also click yes to restore from google backup. After that it successfully restored the old messages and whatsapp was working normally and can see all my old chat history messages.