Failed to execute 'insertBefore' on 'Node'

[car12o]

Description

Hi all,
Yesterday's release (2.3.0) broke the element styles process on element-mixin.
We were using 2.2.0 and today we updated to 2.3.0, some components show this error:
Uncaught DOMException: Failed to execute 'insertBefore' on 'Node': The node before which the new node is to be inserted is not a child of this node. (element-mixin.html:429 ) at processElementStyles (http://localhost:3000/static/bower_components/polymer/lib/mixins/element-mixin.html:429:28) at Function._finalizeTemplate (http://localhost:3000/static/bower_components/polymer/lib/mixins/element-mixin.html:646:11) at HTMLElement._initializeProperties (http://localhost:3000/static/bower_components/polymer/lib/mixins/element-mixin.html:587:26) at new PropertyAccessors (http://localhost:3000/static/bower_components/polymer/lib/mixins/property-accessors.html:147:14) at new TemplateStamp (http://localhost:3000/static/bower_components/polymer/lib/mixins/template-stamp.html:121:5) at new PropertyEffects (http://localhost:3000/static/bower_components/polymer/lib/mixins/property-effects.html:1134:9) at new PolymerElement (http://localhost:3000/static/bower_components/polymer/lib/mixins/element-mixin.html:555:9) at new EdiBase (http://localhost:3000/src/elements/edi-base/edi-base.js:4:5) at new EdiSectionHeader (http://localhost:3000/src/elements/edi-section-header/edi-section-header.js:6:13) at EdiModules (http://localhost:3000/src/elements/edi-section-header/edi-section-header.js:60:20) at http://localhost:3000/src/elements/edi-section-header/edi-section-header.js:61:3

Weird that only affects some components

Browsers Affected

• Chrome
• Firefox
• Edge
• Safari 9
• Safari 8
• IE 11

Just tested on selected ones.

Versions

• Polymer: v2.3.0
• webcomponents: v1.0.20

[TimvdLippe]

Thanks for reporting! This is a duplicate of #4975