Iphone7 Whatsapp stuck at uploading backup to iCloud

I was trying to log out iCloud & log in again, the backup is successful but uploading is stuck at 52.4MB of 4.6GB despite my iCloud still have more than 8GB, internet connection all in good condition.

Or is it if too many message on WhatsApp, the data is unable to restore one?

Anyone encounter the same error? Please assist to help me resolve the issues of migrate old phone WhatsApp info to new iPhone. Inside has a lot of important info where conversation between customer is inside.