Sorry we have not received similar reports from other customers. When you double click to open a file in the cloud drive, the file is downloaded to a local cache folder. If you close the file without any changes, then the file size and last modify time should not change. Please verify it is true. If so, if you double click the same cloud file, then it will not be downloaded again as it is already cached locally.
Could you please test a few other files, incl. Microsoft office files? Let us know if it happens to other files or not. For more trouble-shooting, please send the event log from the Drive Mapping Tool: open the Drive Mapping Tool software window, click Advanced, then click Event Logs -> Send event logs to support.