Some groups are not visible in my WhatsApp
Try the following steps:


Make sure that admin user have your  phone number in your address book.
Ensure that admin user is using WhatsApp Messenger.
Make sure that admin user have the latest version of WhatsApp. 
In admin users Android phone book, make sure that all contact accounts (i.e. SIM, Google, Phone) are "visible" or "viewable".
In your Android phone book, ensure that all contact groups (i.e. Friends, Family) are "visible" or "viewable".
You can make your contacts "not visible" and then "visible" to force a refresh. After doing this launch WhatsApp > > Menu Button > Refresh.    
Alternatively, you can use all your contacts, not just the "visible" ones. To do this go to Menu Button > Settings > Contacts > Show all contacts.