There was a bug in the code, when you want to plot the antenna gain using imagesc function, with different UE height values, an imaginary number was generated that caused this error only when plotting. The bug is fixed and you can re-download the simulator, or only replace the file +macroscopic_pathloss_models/generalPathlossModel.m with the updated one.
Regarding UE height, note that the given parameter LTE_config.rx_height is only an initial parameter. There is a so called UE_height_map that is generated in +macroscopic_pathloss_models/generalPathlossModel.m with the actual height values for each pixel (a map with the same size as the pathloss map is generated for UE heights). This is generated based on the 3D model specification, depending whether the UE is LOS or NLOS, so if you look at the code, with the value LTE_config.rx_height are determined the NLOS pixels in the map, that is why it was set 1.5m according to the standard. However you can modify the height map without restricitions on its values.