New Mini V-Wheels not Runing Smoothly

Hello, I am from Croatia and am new here. I am currently building my first CNC machine and have noticed that approximately 30% of my polycarbonate extreme v-wheels does not run smoothly. When I roll them by hand, the resistance I feel is not continuous, It rather feels like crackling so to say for a lack of better word to describe it.
It does not seem to affect functionality at the moment but I'm wondering if this is normal. The wheels were bought 2 years ago but never used. Does anyone have a knowledge about this?

 

I am just doing some investigation on the issue and found out that the problem disappears when adding 1 additional shim between the bearings. So with two shims between the bearings the wheel rotates smoothly. My first thought was that the polycarbonate part of the wheel was not machined well enough, so I went to take some measurement. It showed up that the bulge inside the polycarbonate part that centres and keeps distance between the bearings is 0.1 mm thicker than the shim. Shim is 1.02 mm thick while the bulge inside the is 1.13 mm.
I don't know if this is a problem. The problem appears only when the wheel is screwed down with the polycarbonate part in its place. Same assembly but without the PolyC. part only bearings and the shim and the problem disappears.
There is also one other potential issue. Many if not all polycarbonate. parts have some small cracks especially on the bulge inside. They were from the first moment I get them there and did not look very malicious so I assumed they are normal. Now I am not so sure anymore. Ill put some pictures...

 

What I would like to know is if those are real issues and should I try to sort it out with my supplier

 

Problem with crackling/discontinuous resistance solved. I could not believe but it turned out Gary Caruso was right. The bearings were not pressed sufficiently enough. My fault.

The only thing that still worries me are those cracks. ( see img) Hope they are not going to spread.

 

The issue seems to come back each time after I mount the wheels on the c-beam and try to mimic workload by applying some reasonable force by hands. After that, most of the bearings become dislocated again and the wheels do not have to be taken off the plate to relocate them, some just need to be pressed toward the plate while others need to be pulled from the plate to hear the "click", the sound of getting them into place again. After that, they run smoothly as long as they are not exposed to some workload.

When analyzing the problem I found that the issue originates from the fact that bearings have some free play. It's stator versus rotor wiggles a bit and therefore when a wheel is mounted, the rotating part of a bearing has some freedom to leave it's position while under a workload. Right now I'm measuring the free play of a bearing; the oscillation of the rotor /stator parts relative to each other amounts 0.24 mm... (+/- 5%)

I want to believe this is not the norm
However, I'll have to talk to my supplier
Ps. Video attached

 

Thank you MaryD, I am in contact with my supplier, European distributor...
Cheers