Failed to decode downloaded font, OTS parsing error: invalid version tag + rails 4

Question

I got the exact same error, and in my case it turned out to be because of a wrong path for the @font-face declaration. The web inspector never complained with a 404 since the dev server we're using (live-server) was configured to serve up the default index.html on any 404:s. Without knowing any details about your setup, this could be a likely culprit.

If running on IIS as the server and .net 4/4.5 it might be missing mime / file extension definitions in Web.config - like this:

<system.webServer>
	<staticContent>
      <remove fileExtension=".eot" />
      <mimeMap fileExtension=".eot" mimeType="application/vnd.ms-fontobject" />
      <remove fileExtension=".ttf" />
      <mimeMap fileExtension=".ttf" mimeType="application/octet-stream" />
      <remove fileExtension=".svg" />
      <mimeMap fileExtension=".svg" mimeType="image/svg+xml" />
      <remove fileExtension=".woff" />
      <mimeMap fileExtension=".woff" mimeType="application/font-woff" />
    </staticContent>
</system.webServer>

I was having the same issue., OTS parsing error: Failed to convert WOFF 2.0 font to SFNT (index):1 Failed to decode downloaded font: http://dev.xyz/themes/custom/xyz_theme/fonts/xyz_rock/rocksansbold/Rock-SansBold.woff2

If you got this error message while trying to commit your font then it is an issue with .gitattributes "warning: CRLF will be replaced by LF"

The solution for this is adding whichever font you are getting the issue with in .gitattributes

*.ttf     -text diff
*.eot     -text diff
*.woff    -text diff
*.woff2   -text diff

Then I deleted corrupt font files and reapplied the new font files and is working great.

I had a corrupted font, although it appeared to be loading without problem and under Sources in Chrome devtools appeared to display, the byte count wasn't correct, so I downloaded again and it resolved it.

try

@font-face {
  font-family: 'icomoon';
  src: asset-url('icomoon.eot');
  src: asset-url('icomoon.eot?#iefix') format('embedded-opentype'),
       asset-url('icomoon.ttf') format('truetype'),
       asset-url('icomoon.woff') format('woff'),
       asset-url('icomoon.svg#icomoon') format('svg');
  font-weight: normal;
  font-style: normal;
}

and rename your file to application.css.scss