Monarch users could experience performance problems if they have a project saved with multiple summaries, data views and reports opened in it by default.
When project is opened - Monarch will remember those windows were open and proceed to build and display them again. Multiple, simultaneous summary builds is expensive, resource-wise, and will drag any machine to its knees.
The workaround is not to have so many windows open when you save the project.
In contrast - Monarch 10.5 would only let you open one summary at startup.