okay, you found the nexus
the nexus does not work like normal memory
you can allocate memory, but you can never give it back to reallocate it

so the solution for you is the reusing of your segments
just store all entities an array and shift through them
if you "remove" an entity, just set it to invisible and passable
if you use it again set it to the wanted position and show it again

Tricky indeed! Thanks for the tip! Have a Merry Christmas!

yeah, but the nexus is pretty fast compared against other memory allocation systems
so if you don't exceed the nexus you can get really fast results allocating memory
but only level_load will release it again