When I try to use the /give command below in 1.12.2 with a banner, it works fine. The same command generated this error in 18w19b

Also the item minecraft:banner does not appear in the list when typing the command.

In a command block try this.

/give @p minecraft:banner 1 0 {BlockEntityTag:{Base:11,Patterns:[{Pattern:tts,Color:3}]}} 

[00:32:13] Unknown item 'minecraft:banner' at position 8: give @p <–[HERE]