I'm going to go WAY out on a limb, and dust off some fundamental English grammar.
"Complex" is an adjective. It describes an inherent property. Example: Some systems are complex.
"Complicated" is used as an adjective, but it is in fact the past tense of a verb, "to complicate". Example: This mess is complicated because 47 different managers all worked overtime to complicate what should have been a simple CRUD app.
When something is complicated, it is because some other agent has worked hard to complicate it. (This usage also appears in the medical field.)