Impossible de sauvegarder

Hello, since yesterday I have been trying to create a maintenance page for my website. I used the same plugin as usual, but it doesn’t work.
I tried 10 other plugins and it doesn’t work either. Every change I make doesn’t save! Even if I hit save…
I tested creating a page directly on my site, without a plugin, and it’s the same thing. I can’t do anything because when I exit, after saving, the page is empty…
Do you know where the problem could come from?