Yes , there is a conflict with your template's bootstrap's modal css class.
It requires you add additional CSS the plugin style.css file.
Code:
#vm_qrcode a{
position: relative !important;
display:block !important;
}
Let me know if this is better.
Also I see you duplicated the plugin css to the virtuemart css file. This is confusing and could lead to conflict.
Is there a reason for this ?