When I created the gerber from my project, the initial preview of it was okay, but the generated gerber file had several letters missing but not all the same letters.  The bottom of an i, the letter h, but then elswhere the same letters would be there.  Maybe one or two out of every word.  I was using a font called Bungasai and another called Playball, both had letters missing but in different ways in the final gerber.  I ended up switching to a third font called Bitwise which corrected the issue.