Unbalanced weights can be a real problem.
I went for the Aquarium dive at Disney World in Orlando. At the last minute they decided the BCD they had fitted me with was too small so they quickly changed me over. Once I got under the water, I found two problems. 1- I sank like a rock and 2- could not keep from rolling on my side. I was a very new diver so I just chalked it up to my lack of skill. It was a very difficult dive, I was flailing all over the place. I'm sure my buddy thought I was a total dorf.
When I got out I pulled my weight pouches. One had 5lb, The other had 15lbs. Yep it can roll you right over on your side.
I've become a lot more assertive since then. Twenty feet in an aquarium wasn't dangerous, but in open water it really could have been. I now take my time and check everything. By the way the Aquarium was a blast otherwise. I plan to go back.
Hyrum