Flight Level Separation

I’ve noticed that on nearly every airliner flight I do, I encounter, at least, one aircraft at my flight level flying directly towards me. Often these aircraft are within frighteningly close range.

I use Real-Time Online air traffic.

It is my understanding that flight levels are divided by odd/even for 0°-179°/180°/359° courses.

Does the sim (ATC) not recognize this? I’m confused as to why this continually happens.

Does anyone else note this behavior?

They’re probably climbing or descending. I’ve had it happen a lot too and it’s fun to see how the planes respond to RAs.