A lot of people talk about lateral shifts in the squat, but this problem happens in the deadlift too. It happens when the lifter shifts more weight to one leg than the other.

There can be multiple reasons for this issue, but in my experience the majority of people can fix this over time with two things:

1. developing awareness of your weight distribution from right to left

2. improving muscular tension and activation on the weaker leg and learning how to maintain that throughout a full range of motion.

If you have this issue, expect to spend at least 4-8 weeks working on fixing it; it’ll take this much time to develop good control at heavier and heavier weights.

The length of time really depends on your level of body control. If that's not at a high level, you may have some remedial work to do first. Check out my blog post on glute activation for that.