CAPTCHA form not visible, after applying theme
I was facing the same issue before and in my case it was caused by my theme's customer_account_login.xml
file.
For example, if your theme is extending Magento_Blank theme (which in most cases it probably is), then you don't need to copy the entire contents of the customer_account_login.xml
file to your theme to make changes to it --> this will just "bug out" the CAPTCHA form.
The proper way to make changes is to use:
<block
and<container>
elements to add new elements (blocks or containers)<referenceBlock>
,<referenceContainer>
to add new elements to existing ones, change their properties or just remove them<move>
to move existing elements in the layout
You can read instructions here on how to do that: http://devdocs.magento.com/guides/v2.3/frontend-dev-guide/layouts/xml-instructions.html
If you are facing the same issue, you can quickly test it by renaming or removing your theme's customer_account_login.xml
and clearing cache.
Then you can make the customizations the proper way based on the official documentation.