Here's the dop network during Applied Houdini Rigid III. In (SOP Solver), there is a simple VEX i@active=1; which helps sim to take over from animation.

I thought bypass (Enable Solver) should be equal to connect (SOP Solver) directly to (rigid Body Solver), but actually they turns out different result. The former leads to animated result while the later make packed object free fall at the very begining. It makes me so confused.

So, does bypass (Enable Solver) means nothing will be enabled, rather than simply ignore (Enable Solver)?

And, if my guess is right, which other nodes also have this kind of bypass issue?

Many thanks!

When you bypass an enable solver Houdini doesn't remove it form dynamic context instead it changes its datatype from SIM_SolverEnable to SIM_SolverStatic means that if there is a static solver instead of enable solver.
As a static solver does nothing at all and it doesn't let information to pass and send to rigid body solver.
This is why you get just an animated object when bypass Enable Solver!
I don't know why SideFX chose this odd way!
It would be great if one of their developers explains the reason.