Ideally, there is another module, js script catch event Click on Login button. So, we should disable them like above comment.


How to fix


Solution #1: 


Open file: app/design/frontend/Smartwave/porto/Smartwave_Porto/layout/default.xml


Remove:

 

<block class="Magento\Customer\Block\Form\Login" name="header_customer_form_login" template="Smartwave_Porto::html/login.phtml"/>

 



Solution 2:


Open file: /view/frontend/layout/default.xml


Add the following block XML in body tag

 

 

<!-- Fix Popup login -->
<referenceBlock name="header_customer_form_login" remove="true"/>

 


 See this file