Males of all loricariids are territorial. Some species much more aggressively so than others. Given the mature size of the common pleco, Hypostamus plecostamus, I would separate them sooner rather than later. While the common is growing, even if no actual physical encounters are observed, it is sending out chemical signals of its territory, and this could stress the smaller Bristlenose (Ancistrus sp.).
It is a common misconception in the hobby that species which are not compatible at maturity can somehow be housed together while young, but this is a mistake. Such species should never be together in the same tank, unless of course it is enormous.