Unable to Save – textbox

I’ve taken over support for a site that I didn’t build.

Weird issue that I’m unable to Save a textbox in the Visual Builder. The textbox box opens but no content is shown if I click on one of the other tabs, then go back to the general tab, the content appears again.

I bought the theme, updated all the plugins – same problem.

WordPress 4.9.6
Php 7.0.30
Fortuna 2.10

Tried deactivating plugins but nothing seems to work. I’m a bit lost as to what’s causing this.

Chris