Some light sources reflections aren't calculated

Hello,

I'm spawning a lot of cubes, all containing a Point Light source inside it. But at some point, some light sources stop reflecting on the ground.
I saw that only a few of the lights inside the camera's view are displayed correctly.
Is it possible to calculate all of them ? Is it too much computer intensive to have 50 of them in a single scene ?

You'll see exactly what I mean with this clip :

Thanks for your answers!

 

Try deferred rendering pipeline