question about showdow in the Warp and the hivemind

I know that during the opening of the great rift, the tyranid forces where heavily effected.

So my first question is that I thought that shadow in the warp would protect them from such effect of the warp

2. If the hivemind was effected that much by the event in the galaxy, does that mean that the main force of the tyranid is already here within the galaxy

3. How strong is the hivemind in general, is it as strong as a chaos god or even stronger?