Plants which grow verrrrry slowly are prime targets for BBA. Anubias leaves seem to grow to adult size, then just sit there watching other leaves grow. Those leaves that are just sitting there always get BBA in my tank, even with low light, 20-25 PAR, with daily 5-8 ml dosages of Excel. I cut those leaves off when they begin to offend me, but eventually other leaves get it too, still only those leaves that are not growing.
My anubias are anubias nana, about an inch high above the substrate, so they are definitely in very low light - they are also snuggled up against the Mattenfilter, at one end of the tank, where the light is even lower in intensity. I don't really get bothered by it since I can ignore it for a couple of weeks or more, then trim it off, and it's gone. With high light it grows very fast, making you do the trimming every day, and that is still not enough to slow it down.