Those sources I've found report that Kazakhstani bailiffs put an arrest to Russian property (basically they can't move it out of the country) and forbade some manager to leave country as well. I'm not sure if English meaning of word seizure includes those actions, I thought that seizure is more like expropriation and that's not what happening here.
I think that's not serious. It's either some politics or just bureaucracy. While Kazakhstan is not fully supporting Russia, turning away from it seems like an economic suicide.