Power struggle refers to two people in a relationship fighting about who is in control, with both trying to dominate the relationship in one way or another. Switch out power for plant and you have the definition of the problem in using ayahuasca and marijuana together.
Cannabis is a master plant. Master plants are the most intense of plants, the strongest of medicines and do not always combine well. In the case of cannabis, it works in a far different manner than ayahuasca. The shamans describe it as a plant with two faces. One face, the happy face, makes you feel good, relaxed, silly, etc. On the other face, it can cause anxieties, depression, compulsiveness, paranoia, mood swings, etc. The spirit of the plant is wavering depending on the person and for this reason it does not go with the ayahuasca.
It is recommended if you are going to insist on using marijuana in the future, to do this in a personal ceremony. Give thanks to the spirit and make it a special moment, even a small ceremony. Using this positive intention you are more likely to get positive results from the plant.
Santo Daime, the well known brazilian ayahuasca church, does not support using cannabis in ceremonies or outside of them while practicing with ayahuasca.
While marijuana most certainly has important medicinal uses and more, it is necessary to respect the master plant and its power. Any master plant used outside of its intended purpose is not recommended.