I got you, but in fact that problem happened too recently, everything was good since last time I used After Effects.
What exactly happens that any empty space in the timeline, it isn't normal black solid, no, it's Fractal Noise, yes even the blank space in the timeline, no element and nothing there.
Check the timeline marker, it's on nothing.

What can it be Mr. Dave?
I appreciate every word from you.
Best,
Yazeed.
Perhaps it's a caching error.
Purge your cache with Edit/Purge/All Memory and Disk Cache
Also try restarting your machine.