Janet's London custody case is contentious ... not because either parent thinks the other is unfit. Our sources say Janet's having trouble because she wants 1-year-old Eissa in the U.S. with her. Problem is ... Janet chose to move to London to be with Wissam and that's where Eissa was born. It was her decision to move back to the U.S. after they broke up, and that may be giving Wissam the edge.

Janet was indeed upset with Wissam over the weekend and we've learned she called the cops twice -- once on Friday and again Saturday. Thing is ... it was all about Wissam not making Wi-Fi available to Janet's nanny because cell service was spotty in Malibu and Janet wanted communication.

Stories initially surfaced that the nanny became frightened by Wissam's "aggressive behavior." The way the initial story went ... she was "terrified by his behavior and locked herself in a bathroom so she could contact Janet." That story did not come from Janet ... it came directly from her brother, Randy.

Sources connected to the former couple say Randy is fanning the flames of conflict to help Janet gain an edge in her custody case. They say her call had nothing to do with a terrified nanny. It was all about cell phone service, although she did drop a reference to drug use.

We're told cops went out and were literally there only a few minutes before they realized nothing was wrong and told them to deal with the cell phone service issue themselves.