spawn from character class and parented with it

hi guys, actually me and my friends are trying to make a game that is a little ambitious but we met a strange problem, actually i tried to make in c++ a for loop that spawn actor, but everytime unreal reach 10 character class or derived inside the same map it stop to spawn, i tried even in a new project that was blank to make it in the same way (for loop that spawn enemies).
after some test we noticed that after reached the number of 10(player + 9 enemies) it start to spawn null actor as you can see in the photo


this happen only in a single spawn, every spawn point can spawn max 9 character class or derived, if i want more i need to put more spawn point into the map, how can i solve this?