hmmm, what you describe is beginning to sound more like some kind of memory leak or recursive function running away with itself, rather than an issue in the 3D render pipeline, or perhaps some issue in the delta being calculated for the animation mixer. Could you post the content of your equivellent to the animate() function? The code that handles your render-loop.
My suspiscion is that either there’s something wrong with the way you’re reading the delta for the mixer, or that there’s some kind of recurssive function call.
It might be an idea to get the Task Manager open - the one inside your browser (both Chrome + Firefox have one in their More Tools menus) and see if the CPU/RAM starts running away during runtime.