Russian 20k, Are The Highlighted Considered As Serious Errors? Thanks

Robi, the only thing I can see here is mis-registration. These stamps were probably printed in more than one press runs, maybe as much as three. The clearest example of this mis-registration is where the blue line are printed into the red field in the middle. Is that what you are asking?
It is not considered an error - more like an oddity or a freak. Your example is pretty bad, some people collect stuff like this.

Peter

Petert4522,
do you see the darker lines (looks like many X's )? And also if you see the difference in color inside the gray highlighted area?

I see what you mean. I would have to compare this to another one, but I do not think this is unusual

Peter

I would kindly ask you to do, I'm really curious to know your opinion after comparing