Often when I put my X220 to sleep, after a few minutes I can 'wake' it up and it resumes from Sleep mode. But then there are other times when it goes into Sleep mode and after about 10 minutes I notice the Sleep light isn't flashing when I attempt to 'wake' it up, but is totally off instead.
When I press the Power button it resumes from Hibernation and not Sleep mode.
I always press Fn+F4. What is the issue here?
You may have enabled Settings in your Power Profiles for Sleep and Hibernate timeout.
"Deep Sleep state is a low-power state supported by many modern x86 microprocessors. In this state the CPU core maintains its context, core's internal clock and the clock of L2 cache are stopped, and the core may not respond to interrupts and other signals. This state is always entered from Sleep state. In some CPU families, like Pentium III Tualatin and Coppermine processors, Deep Sleep state is the lowest power-saving state. In other, more modern families, the CPU may transition from this state to Deeper Sleep mode which has even lower power consumption.
Deep Sleep state provides better power savings than the Sleep state, but transition time from this state to normal operation mode is even slower than for the Sleep state."
Check your settings in the Power Profiles and make the necessary adjustments for when you want your machine to get into Sleep or Hibernate mode.