My caged life.

Your pictures give a clue to the potential problem, but you'll have to carefully measure your device to be sure. Another way to discover the exact problem is to wear the device and gently twist and squeeze your balls to manipulate and discover where and which one will squeeze through the gap.

From the shapes of the ergonomic base ring and the tube ring, it seems to me that the gap isn't the same all around from top to sides to bottom. What often happens is that when a chastity cage is hanging straight and square, and your testicles are too, then the boys are hanging side by side at the bottom. This means that each of them is offset from the bottom centre of the rings.

The gap around the ring nearly always varies in size, and because of the geometry of having the two rings of different sizes joined at the top, the gap around the rings for your scrotum to pass through is smallest at the top, getting wider as you go down each side to being the widest at the bottom. Another consideration is that the testicles are rarely the same size, one is usually a little bit smaller than the other. They're also compressible, a little without pain, a bit more with pain, so each doesn't have a fixed size anyway.It might be that the smaller one can squeeze through, while at the same time the larger one gets pinched.

So, everything staying hanging straight is ok, but we move around a lot every day, and so does your cage. If a testicle (maybe only the smaller one) lines up with the widest bottom part of the gap then there's the opportunity for one to slip through.

The best solution is to have a design of base ring and cage ring such that the gap is exactly the same size all around the rings. Unfortunately, most devices don't give this. The design of your ergonomic ring improves the interface between the base ring and your body, but with the bottom of the ring bent away from the cage ring, it actually makes the gap design flaw of having non concentric dissimilar size rings even worse!
The problem with "ring sizes" is that you can actually have a device that while it's narrow enough to pinch at the sides, the non-parallel gap will simultaneously betoo die to constrain your balls at the bottom!

One potential solution is to use a strap around the waist to hold the base ring close to your body. What this also does is prevent the cage turning, so avoiding the ball to gap bottom alignment. That could be fabricated by preference by anything from a simple thin ribbon, leather or fabric straps, to a lockable chain. Holding everything straight and close can go a long way to eliominating the problem, but the best solution is having a uniform gap.