I am experiencing the exact same thing described in this post: https://discussions.apple.com/thread/250390803
It started as soon as I upgraded from High Sierra to Mojave. After a long sleep (30min-2hrs), the wake hangs in a black screen for a while before the screen turns on and shows inverted, distorted/pinkish colors while everything remain frozen.
After keep pressing keys in the keyboard between 30 secs to a minute, then it wakes up completely.
- Activity monitor shows that there is 4 out 8GB free memory.
- I've already reset NVRAM and SMC.
- I've reinstalled OSX Mojave.
- I've installed an OSX update that specifically called out problems with the system waking up.