When a enemy like web shooter spitter that deals one type damage and immunise that type was conversioned from group of same type enemy, they attacks each other eternity.

I don't know if there is a solution this this...
They are Immune to each other, so they can't kill each other....

I'll have to think of a solution, but don't know what can be done right now.

If they don't need true immunity against attack of themselves, decreased resistance percentage by a few point or making their attack have slight sub damage type might resolve this problem.

note
"Minelayer Spitters VS Minelayer Spitters" makes huge amount of stacked spitter mines in 1x1 area.
When I killed they who spitting Spitter Mines against conversioned friend, I faced crash error often randomly.

Stack trace is here.
Error while running event.
Natural_Evolution_"Buildings"::on_entity_died(ID4)
Natural_Evolution_Buildings/control.lua:498: in function
<Natural_Evolution_Buildings/control.lua:410>
[C]: in function 'index'
__Natural_Evolution_Buildings/control.lua:498
<Natural_Evolution_Buildings/control.lua:410>

The above crash should be fixed with 0.17.9 release of NE Buildings.
It happened when a turret ran out of conversion inventory.