What hind-end wobbling usually means
Wobbling, swaying, weaving, drifting, or feeling unsteady behind usually means the horse is struggling to organize the hind limb chain. Sometimes that comes from plain weakness. More often it comes from discomfort, fatigue, compensation, or a movement-control problem.
The most useful question is not just is the horse wobbling. It is when does it happen. Does it show up on circles, in transitions, backing up, uneven ground, hills, after the horse has already worked for a while, or alongside hind toe dragging. Those details help separate a mild stability issue from a bigger one.