My phone had a problem so the mobile repairing center did factory reset. Then I reinstalled whatsapp and tried to restore backup from Google Drive. It took about 1:30 hours for 400 Mb and didn't show any indicator for what percentage it has completed. So I just tapped home screen and then tapped whatsapp. It showed me a new window of entering my username and took me to chat window. There I saw no previous chats were present, just 2 old groups and also no messages in them. I again Uninstall and reinstall whatsapp it didn't show me 420 Mb data size, it asked me if I want to recover today's messages. Can you please tell me can I get my backup from Google Drive again?
It happened to me also, I guess it's a Whatsapp backup and restore bug, I tried to upload my backup to Google drive which is 600 MB in size and it took more than 12 hours on 1 MB/s network. I can confirm this bug was not present in previous versions, so only thing we can do is wait for Whatsapp developers to fix this annoying bug or going back to previous builds where the bug was not present. Hope you find this useful.