The GroundMat study was able to finish although it took several hours to complete. However the Earth Potential, Touch Voltage, and Step Voltage took several minutes to load (more than 15 mins on some). This is due to having a large amount of data to load (several hundred MB of data) - caused by the very small intervals set in the study options shown below. The study area is about 220m which has to generate points in 0.05m intervals. This is very small which will cause to slow down the study and loading process.
Try increasing the interval to 0.5m or 1m. The study will finish faster (minutes compared to hours) and the loading time is almost instant.