Yes.
It builds up thickness, so you can't use it anywhere that slides or has to fit. It doesn't hold up to sliding wear on non-critical mechanical interfaces.
In order to get it to stick to metal and not just flake off, you have to do a serious abrasive blast. That totally obliterates any original surface qualities as well as any galvanic protection or conversion coating that may have originally been there. Because there can't be any galvanic protection, the Cerakote is completely vulnerable to filiform corrosion starting at the edge or any other place where the coating cracks, chips, gets scraped or just has enough porosity for chemicals to get through.