Drive Mapper is an API driven tool that only caches local data, and the files seen in the directory are often not actually housed on your local computer. Many users sometimes fail to understand that actions they perform will not be as responsive as in other areas of the File Explorer, seeing as how they are dependent on network activity. Frequent directory changes and working with larger/numerous files will affect how the program functions.
The application is fastest when you are navigating among common drives, the size of data which is less than the cache setting. When you exceed that setting, Drive Mapper has to dump data to make room for more data, and files or folders that you were using and accessing very quickly are now much slower, as the application has to re-download the associated files. Having an increased cache will help you keep more data on the machine and improves performance.
Regularly restarting the affected computer on at least a daily basis, and verifying the version of software installed is the most current, are recommended.