At a guess, I'd say that the acryl softened the printed legend, and then wasn't thick enough/hadn't fully dried/both and wore through quickly, taking the legends with it. I haven't heard anyone else complain about the legends on any boards wearing through that quickly.
As a solution, I'd probably sand off the rest of the legends, find decals of a font I linked, put them on and then coat them with several layers of acryl, thinned clear nail polish or lacquer, making sure to let them dry completely between coats.
Or, alternatively, dig up some double-shot or blank keys.