Revolvers are plagued with a number of problems just like every other firearm.
None of them are 100% reliable.
A couple of these problems I think should be considered by those who choose to carry one for bear defense.
1. Lightweight revolvers using "hot" loads can set the bullet forward of the crimp. This will pretty much render it useless until you have the tools to fix it.
2. "hot" loads can cause the primer to flow into the firing pin hole. Cylinder will no longer rotate. This happened to me shooting +p ammo out of my wife's .357.
Both of these issues apply to bear defense ammo and revolvers.
3. loose ejector rods.
4. Dirty revolvers have plenty of problems, and my sidearm gets pretty dirty at times.
5. This is debatable, but imo, revolvers won't take the abuse that an auto will, either way, revolvers can be damaged and rendered useless if dropped.
6. Some people tend to buy into the myth that revolvers are fool proof marvels of engineering that don't fail. So they fail to test them. I was guilty of this myself.
I won't carry an automatic without firing 400 rounds without failure, but I carried a .357 mag on the blackfoot river while fishing, without testing the ammo. This is the gun that failed on shot 1 when I fired it later. A stupid mistake on my part, but on that can be learned from.
7. Look at an exploded view of a double action revolver, and you'll see that there are more moving parts than you'd think. Several of these parts can and do fail or wear out.
Revolvers are very reliable, but not infallible.
There is no such thing as a 100% reliable firearm of any kind.
Sorry for the long winded post.