I had a closer look and learned this is not a Cite bug. The fact errors are sometimes hidden is a decision entirely made by the English Wikipedia community, via customized messages and templates:

{{broken ref

| other             = <span class="brokenref">

span.brokenref {
	display: none;
}

This issue does not occur in most namespaces, only in a few that fall under "other". That includes the user namespace.

This issue also does not occur in case your user language is not English, because in this case the customized message https://en.wikipedia.org/wiki/MediaWiki:Cite_error is not used, but one of the unmodified localizations, e.g. https://en.wikipedia.org/wiki/MediaWiki:Cite_error/de.

There is nothing a Cite developer (no matter if staff or volunteer) can do about this. I don't even know how to tag this.