Thumbnail role missing in product edit page admin

Question

Update : Now Upgraded to 2.2.2 before it was 2.1.2

ISSUE

I am trying to figure out why thumbnail role suddenly missing when i try to edit a product from admin and want to change thumbnail image also for new products thumbnail role not showing please see attached image

Steps:

1. From Magento 2 admin go to products->catalog try to edit any product
2. Click Images and Videos Tab
3. Select any image which i want to assign as thumbnail image a popup appears with roles but thumbnail role is not here also same happens for add new product see attached image for details.

please advance thanks for help.

Answer 1

now issue is solve in thumbnail image role.

Stores > Attribute Sets > Default > Groups inside image section unassigned attribute drag and drop image section save it before use this command.

php bin/magento indexer:reindex

php bin/magento cache:clean