I also now have this problem, and none of the above suggestions helped. I contacted my organization's internal help desk and they said that Microsoft no longer supports Sleep mode. I do not believe that. What is going on?
Method 1: Sleep isn't listed anymore. "Change settings that are currently unavailable." only shows "Turn on fast startup", "Hibernate", and "Lock".
Method 2: Since it is a company laptop, I cannot access gpedit.msc
Method 3: I haven't tried it yet, but will next. It seems doubtful.
Method 4: I tried it, and restarted, but no change.
Method 5: I do not have a "CsEnabled" option in 'HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Power'