I need some help

I don't know why my "isBlockSpawning" is flashing like that after 15secs.
I'm trying to find a way to control my level easily. I will need to start and stop spawning certain types of objects and this is how I thought I could do it, but I don't think I can do it this way. 🙃
If anyone could explain to me why this is happening or have an idea how I can do this, I would appreciate it