You obviously had some backtests that were tremendously slow
One reason could be the number of trades it has to process.
if the EA trades a lot, it will be slower and slower with the number of trades rising.

one way to overcome that situation :
1) zoom in to the max on the chart (or use the '+' key)
2) resize the window to its minimum
3) minimize the window
4) Change the backtesting Expert tab to the graph but neither the log nor the trades, because they are both slow to display

it will speed up a lot the process

Jeff