W3C validation error on rare conditions.

Validation error: Consecutive hyphens did not terminate a comment. -- is not permitted inside a comment, but e.g. - - is.

<!--[if lte IE 8]>
<link type="text/css" rel="stylesheet" href="https://example.com/sites/default/files/css/css_Gs5lI23oYXOC2YcnSprU--PdK5y-AjxgX9ulnop8bDE.css" media="all" />
<![endif]-->

This is the CSS file that generates 2 hyphens next to each other:

.block-breadcrumb .breadcrumb li:after {
  top: 2px; }

.node-type-process .block-breadcrumb .breadcrumb li:last-child:after {
  top: 2px; }

Note that hash is generated from aggregated file content.