Blank pages in front or admin (WP4.9)


Hi. First of all, sorry if this post is not in the right forum.
I build a website using wordpress 4.9 here :
After upgrading the theme via the web file manager, I get a blank page instead of my site and also have a blank page for admin login page. But I still can access web file manager. Any idea of what happens ?
I notice that my files have a bad date (2018-11-11 00:02:00) but i cannot imagine that this is the reason why it doesn’t work.
Many thanks for help


Hello. Problem fixed. Due to a missing required theme file…