My experimental magnus doesn't work

I just got the exp magnus from a medium base defense mission, i put it into my (4) slot and when i tried to equip it, my character put his weapon away and then pulled it back out again, no magnus in sight. please help

There already is a topic about that.
Please use the search next time.
Here the solution:

Since there’s already a report about this issue, I’m closing this one.

//Mod