Disabling SSL for one page only will not work when the homepage is SSL, after visiting the homepage, the browser will visit subpages over SSL as well. In your case, you have the ssl version of the page in the cache as well.
It’s hard to say what is happening without seeing the website. When the mixed content fixer is active, it will force all resources over https. If that resource does not support https, this might be the result. You could check which url is generating this error by right clicking your webisite, then click “inspect element”, then “console”. You will see more details about the error there.
Problem solved. The bank in test mode don´t let us the HTTPS connection to their servers. However, really Simply SSL always transform that URL to HTTPS (perhaps the PRO version module could discriminate that particular url).
Solution: Simply put (after make the tests with RS SSL plugin OFF) the bank system in real mode the problem is over.