Armature Uneven deforming with Modifiers? I've had a very vexing issue for some time now and I can't seem to find a fix.

I have an armature set up with a mesh (mostly done) but some parts of the mesh deform entirely out of sync, and this changes depending on which of my modifiers are on. I have two armature modifiers on the mesh, one allowing it to deform, and the other makes the mesh track to the armature properly. Both have vertex groups and envelopes on, and preserve volume. The problem is the spine of this model works perfectly with the one modifier, but completely breaks when i turn on the second one. Without the second, the rest of the armature is very messed up.
I've done the weights manually and have tried several layouts for the weights and the bones themselves, but the problem persists. I've even removed the spine completely and remade it from scratch and it still has the same problem. The rest of the bones behave fine so long as the modifiers are on. I have no idea why it would only be one or the other being messed up, since they are both part of the same structure.

I can try and post some pictures if need be, its just very messy at the moment.

Edit: Never shared on here but lets see if this works
One can't parent a mesh to multiple armatures, and 1 should realy be enough.
If there are some small morphing you'd like to do who are because of their detail movement not easily done with bones, you can add shapekeys for that.

Notice its also possible to use bone constrains (often with empties as helper objects) to control you bones, ea i did that in a car rig, just telling because i dont see any reason why 2 armatures would be needed. I made way more complex armatures but have never had a need for it, so it puzzles me why you want it.
Its a but unclear to me, what you try to achieve with it, perhaps if you can explain i might think of another way to do that.