I can confirm this bug; I'm currently playing a game with Songhai and was planning on reporting it myself.
On the start/load screen, the UB's tooltip states it replaces the Market. Additionally, Shrines cannot be built or purchased. Mud Pyramid Mosque never shows up as a possible building. This feels like what happened was that the UB wasn't actually coded to replace the Shrine after the Shrine was removed and an obsolete tooltip was left in, but I'm not familiar enough with the project to look at it myself.
Edit: Added screen shots from a new game to demonstrate bug. Only mods running are Communitas. Map is Communitas.