UI Lag on Art of War campaing and build order custom scenarios

Hi guys. Im having a problem while trying to complete the Art of War tutorial scenarios. Basically, after about 15 to 20 minutes, the UI starts to lag out, making it impossible to play. For example, when i click a TC to create viallgers, the UI still shows me the options of the previous unit or building i selected for like 5 seconds and then it gets to the TC related options.

This lag keeps getting worse as time goes on. I also got the same bug on custom maps for build order training like the Interactive Build Order Guide map pack.