When I was survive at the singleplayer DalekMod (version of minecraft 1.9+) daleks spawn in the world very rarely. I found only 1 dalek in the world. What should I do to fix this bug?

If its a bug in the mod then i’m afraid you can’t fix it but only the developers can. Which Dalek Mod version are you using?

 Now i'm using 48.7 version of the DalekMod