You mean it has the cursor flashing in the top-left corner and just sits there for forever? EvilWM does the same thing most of the time for me, and I don't know what causes it. If you let it sit for a while, it should resume, but that really defeats the purpose of instant-on.
I've discovered that if you press the power button again, it will resume, but then it needs a reboot most of the time to suspend.
If this isn't your issue, I"ll start a new thread about it, as I don't want to hijack yours.