This can be caused by many reasons. The first thing you should look at are automation means, such as Business Rules, Custom Commands or Scheduled Tasks. If they, for example, launch PowerShell scripts, and the scripts do not release resources correctly, this can be a cause for the issue.
To troubleshoot the issue, note the time when aggressive memory consumption starts, and take a look at Adaxes Service Log for events that occur approximately at that time and can cause such an issue. For information on how to view Adaxes Service Log, see the following help article: http://www.adaxes.com/help/?Logging.Vie ... eLogl.html.