you have mentioned that report is hanging designer as well, so it seems that there has some change occurred in the query or else amount of data being retrieved. You would see that designer would be consuming huge memory in task manager
Fire the SQL query to your database and observe how much time would it take to execute. This is just to identify whether the prblem is with the query or else the records being pulled.
In addition to this as the issue is observed with only 2 reports can you recreate the report and observe the behavior.