Fonts work in app, but don't show up in preview or publish

I've seen this issue mentioned with different fonts in several posts, so it's a known issue.  I'm on most current version so there's no update to fix it.  We're using Montserrat family of fonts.  Everything is beautiful as I build, but when I create preview or publish, there is no discernible difference between any of the weights of fonts, or from font with bold applied.  Please help!