It looks more like amarilliia, or pithium? But pithium is usually dark colored? Has me stumped, because I didnt know amarillia could infect cannabis? I guess its possible? In either case, you best hope its not amarillia, because that is a mycelial soil born disease and it means a complete replacement of all soils or dont grow a plant that it can infect. However, I think its unlikely. Might be a fungal infection? Have you had unusual temperature swings or moisture issues? Is you greenhouse venting well? Have any other plants of any kind died near that plant? Was there any warning of a sick plant or did it just die and fall down?
Have you excavated fhe root to investigate the root zone? Things to look for… extreme dampness, foul odors, white fan like fuzzy stuff that looks like mold, any pests or holes, any weavils or larvae. Other roots of other plants with that white staining?
Do that and report back to us!