It would help if you can share a more detailed and accurate description of the problem …
eg the original post states :
None of the apps is accessible, the yunohost dashboard still appears though. A error appears saying something about “nginx” (next time it happens i’ll fetch the exact error message and post it here).
The admin access doesn’t work, that means the admin login screen appears, but it doesn’t login. The admin login site just reappears.
But this is pretty fuzzy and confusing
You need to explain very precisely, for example :
« I open my browser and go to https://something (is it via the domain name ? the global IP ? the local IP ? anything else ?) »
And share any detailed error message that you get, or screenshot