First paper published, follow-up paper rejected by editor as out of scope?
Yes, it is normal that articles get rejected as not in the scope of the journal. Yes, it can take a long time for the people in charge (often doing this pro bono) to get around to take a look at an article.

So you published something related before in the same journal. OK, maybe they just want "new results", not the elaboration/extra details on previous ones. Or they don't want "enhanced computation" (presumably more detailed results), and prefer description of methods. Without an awful lot of additional information, we can't tell. Besides, whatever the case may be, the powers that be at that particular journal have the last say. If we consider it normal or not, is totally irrelevant.