Previewing changes in Customization does not work

I have not be able to see live preview customization’s for the front page since the huge PHP update like a year ago and I don’t know why or if that’s even the problem. I knew there were errors in the theme I bought, development issues, coding errors, The Mill and Mommerce theme, so alas I deleted the theme and deleted all the plugins, then deactivated my woocommerce and literally deleted every plugin to try and get this to work, especially with all the amazing things that can be done in customization now, but alas it still does not work. I have NO idea why and it’s so frustrating. I am waiting for IT with my host to see if they can help me but would so appreciate any light someone can shed to this issue?

RIght now when I am customizing the front page, it just shows the login in page and says I am logged out, even though after I hit save and close – I am back to the admin portion of WP, so I am not logged out….

Ahhhhhh, Please help!!