Softsynth latency: anyone have any insights into this one?

On one projects, my softsynths started displaying latency.  The behavior was odd: if I reset anything (e.g. turn recording on and off) the latency would go away, but as soon as I pressed "play," it would come back.  Some detective work revealed that it was the number of plugins I was using that was causing it: when I disabled them, the problem went away.
   Now here's the puzzler: my I7 CPU meters were barely budging.  So, I was hoping someone more technically minded than me could explain how the plugins were bogging down the machine even when the CPU (and ram) were not showing any overload? 
Thanks!

Yup - some plugins either use look-ahead processing, or or otherwise CPU-intensive, and meant for mixing/mastering, not for tracking.
 
The general approach lots of folks take is during tracking to swap out the latency-inducing plugins with other less demanding ones, then after done with tracking put the real 'meat and potatoes' plugins back in, adjusting settings as needed at that point.
 
Bob Bone
 

I wish Cakeland would have a sticky ion what plugins have these kind of buffers that make it non useable for recording as this question gets asked way too much.

In this case size does not matter. The plug-in by design must introduce latency in order to work properly. Plug-ins like the transient shaper are not intended to be used while tracking.