Parts of characters are getting overwritten.
Example code:
(defn function [mom]
(map
#(make %) [mom dad]))
With rainbowth:

Without rainbowth:

Notice that italics make it worse, but it happens with non-italic characters as well.
On ST3 3083, OSX, MacBook Air 13, relevant settings:
"color_scheme": "Packages/User/Monokai.tmTheme",
"font_face": "Monaco",
"font_size": 12,