I've tried to set up your APP with SHOW LOGIN FORM at the "Display Type" option and the PREVIOUS URL at "Redirect Type" option, but it doesn't seem to work, its behavior it's the same like I'd chosen DEFAULT URL at "Redirect Type" option.
Could you please check it?
The issue is caused due to the content of the customer login page on your store.
To fix the issue, we would like to give you the solution as follows:
Step 1: Edit theme
There is a code line as below:
<div class="customer-login six" id="customer_login">
=> On the same site, it does not allow to have two elements of which are the same ID. On your site, the element form and div have the same ID customer_login
Thus, it caused the issue (since our app uses this ID)
Change ID of div as below
<div class="customer-login six" id="customer_login_container">
Step 2: Go to our app and then press save config
If you need any further support, please feel free to contact us.
We are always willing to support you.