I have seen this opacity issue a few times on Netlify. As it turns out, it’s not a Netlify issue, but you’ve not really told us what part of the text is invisible for us to be able to check.
So, I’ll be telling you the same thing I had told other people. Something wrong happens during minification of the code. Suppose, you have something like
opacity: 100% in CSS. While minification, the minifier compresses 100 to 1 but doesn’t remove the % sign. Thus in browsers, the code becomes
opacity; 1% which is almost invisible. So, I’d say, if this is what happening with you, turn off minification (not recommend), or change your opacity value to 1 instead of 100%.