Thanks for getting in touch. Yes, you seem to have found an issue with the SCLogin module when being used with certain templates. We've been updating the module to make it more compatible while also having less extra/duplicate code by relying on some more standard features from Joomla. However, that seems to have bit us here.
I looked at the HTML on your site and *I think* you already tried another answer in a forum post here to add some custom CSS. I'd ask you to update that CSS slightly to fix your current issue while we investigate a more permanent code fix for a future release.
You look to have added the following CSS to your template:
div#login-modal.modal.in {
....
}
Can you change that selector to:
Let me know if that fixes your issue!
Thanks,
Alex