2 iPads, same iCloud account, but contacts lists are different!
Are both iPads synchronized to the same email accounts?  FOr example, my iPhone only Gmail access but my iPad Pro has access to multiple Gmail and Hotmail accounts.  This could account for the variation.  The only way I know to fix mismatched contact lists is to either export one and merge it into the other one.  I'm not sure how easily this would be on an iPad, but if you can send them both to a Gmail account, Gmail has the ability to detect/merge duplicates, etc.