I never turn my iMac off. When I leave, I turn it's screen off.
BUT
Note: I did an NVRAM, checked my Energy Saving Preferences and so forth. Problem has been on for months.
iMac, macOS High Sierra (10.13.3), December 2015, 16GB RAM
My french is pretty much non existent, but if all you're doing is setting a hot corner to sleep the display, but you're not allowing the Mac itself to sleep, any number of things can cause it to register some kind of mouse movement, which will wake the screen, and since you're not there to move the mouse back to the hot corner you defined, it will remain awake.
Don't worry about the French, Macs have the same interface whatever the system's language ;-)
I've had iMacs for ten years and have always turned their screens off like that without any problem.
Since Power Nap exists, i've been using it without any problem either.
Not sure what you mean by "you're not allowing the Mac itself to sleep". There's nobody around when the screen turns itself on, so no movement or gesture whatsoever. (Also, sometimes I'm on the road for weeks with nobody home).
If somebody wants to help, here's another piece of information:
iMac's screen turns itself ON when receiving a notification from Apple Mail, Time Machine and never turns itself OFF.
The only way to turn it off is to log in and dragging my finger on my trackpad beyond the bottom left corner.
Please note: if I do not turn my screen off, it remains on forever. Taking into account my Energy Saving Preferences (see above), is this a normal behavior?
Please see the two screenshots below
How are you turning the screen 'off' to begin with? How are your energy saving preferences configured?
iMac's screen turns itself on
