Okay, all those informations are helpful to isolate the problem.
When an application gets for some time slow while using it, the reason is often on all platforms another application using most of the CPU power, or the hard disk, or running temporary with a higher task priority than all other applications. The Mac Task Manager
could be helpful to find out if this is the case on your Mac when UEM becomes suddenly slow on user actions. I found by chance also the article configd: Fixing High CPU Usage Problems with the configd Process in Mac OS X
which is an example for such a "problem source".
Another common problem for an application response decrease with LAN and WWW connection being active is a temporary network problem. You wrote that you are editing files on local disk, so this common problem source should not be the reason here. But if you have the File View
open and UEM refreshes the list of directories/files in this view and there are mounted shares, it could be that a temporary network problem or the opposite a high network activity results in long delays on reply by the file system on the function calls by UEM. I don't know if the IDM developers have put reading in volumes/directories/files for the File View
in a separate thread so that the user interface of UEM remains responsive for user actions even on file system delays because of slow network responses.