First thing I'd do is look on the bearing (or the box they come in) and see where the bearings are made. If they're Chinese-source bearings, I'd say "there's your problem!"

After getting a hard lesson in the reality of Chinese bearings, I now use only Fafnir disc bearings with the triple-lip seal, regreasable.

As a secondary issue,  I don't tolerate Chinese bearings in any application any more. They're crap, period, full stop, end of story. The Chinese make the cheapest bearings on the market. Once you've used one, you know how they do it.