Changing page templates multiple times within a Design will eventually cause the map window, or map canvas to fail to redraw. This happens in a Citrix environment. ArcMap does not lock up and is still functional, the map just does not display any content.
A custom subtask associated with a task (toolbar button) caused this. The Enabled method of this subtask had additional code causing extensive processing every time it was called.
Do not put database, CPU, or memory intensive code in the Enabled method of subtasks, ICommands, or anything with an Enabled method. If the code must reside in the Enabled method, cache it and make it as optimal as possible.