I got the problem with NPC in generated structures like castles, camp and etc. Minecraft shows their names, but they are turned to blocks and have no texture. However, when I try to spawn them myself, they appear normally. So what is the problem?

And I am guessing you're in creative when they "are turned into blocks". That's because in creative the entities are not spawned in and stay in the spawner blocks. They will only spawn if you're in survival.

Oh, THANK YOU! And is there way to make them spawn in creative?

No there isn't. Why would you actually need that to happen?

Also I am closing this as it's not a bug.

Ok, but it would be better if you mentioned that in the description of mod.
Thank you!

For the future