Looking at the datasheet and looking at the adafruit library, it doesn't look like the library is directly compatible with your board. To get into bitmap mode, you need to send a specific command. The reason it works with everything else is because the printer is set at defaults at power up and accepts your text.
Page 14 of the datasheet describes how to use the bitmap mode. You have to send ESC (27) then * (42) then a mode of 8 or 24 dots, and then your actual bitmap information. I don't see the library sending all those commands.
This was only a quick look, but I don't see it controlling the printer in the same way as the datasheet. However, some of the commands are the same, but those are for text stuff. The barcode and bitmap routines are not doing things the same way.