I know that it is not a good practice to open a new ticket about the same issue, but until now the only answer I've got from Michael Bissett is: "...May I ask if a conflict test has been done yet? I haven't been able to replicate this error yet over on my own install..."
I've answered that I've done all tests (including disable all plugins directory and change theme) and also left open access to my dashboard, but until now I haven't got any new answer.
So: serious problem is that I cannot save my work. It sunddently stopped to work: I cannot save any modification. I mean: not any: no text modification, add, menu and so on.
It seems it saves, but when I test page or I reload Upfront there is not any modification saved. By the way: I've updated themes, maybe that it does'nt save after this update?
I have the same behaviour with all upfront themes but nowhere else with standard WP themes like twentysixteen.
I've opened dashboard access so you can test there and you can do everything you want using this site: http://xmodular.net/test/
I send you screenshot.