Hello!
I think I reported this issue in the old forum but seems like after almost 2 years of not working with SPPageBuilder nothing has changed from the old issues - including the com_media default path (but it's is another issue).
When editing in the front end, try to hit the Editor Close button in the bottom left and notice the URL query string. All of the ampersand will be converted into & html entity code. But before you test it, you have to disable Joomla SEF. Well, I am in development mode so I am switching back and forth to SEF and non-SEF.
In components > com_sppagebuilder > controllers > page.php @line #278, an easy fix to this that I don't think will create an issue but fix the URL query string problem instead.
$this->setRedirect(htmlspecialchars_decode(base64_decode($return_url)));
Simply adding the php function htmlspecialchars_decode() fixes it. The problem is base64_decode() function converts special characters into a html entity so convert it back into a special character.
Helpdesk support please, let your dev team know about this. There's no problem with it when Joomla is in SEF mode but when in development, it's just a pain when modules in the page is not showing up because of the url query string.
Thanks,
Jackson