The knowledge base has a relevant answer only in part.
For slow DSM web interface response, the listed steps are:
- Check Indexing services:
- File indexing: Go to Main Menu > Universal Search > Preferences > File Indexing tab, then Indexed Folder List > User defined and delete the indexed data in all shared folders.
- Media indexing: Stop the media packages listed in Package Center > Installed.
- In Control Panel > Security > Advanced, unselect Spectre and Meltdown Protection.
- In Control Panel > Info Center > Device Analytics, unselect Enable sending device analysis.
- In Resource Monitor > Task Manager > Services or Processes, stop the service or process that makes CPU or Memory utilization extremely high.
- Check Resource Monitor > Performance > Volume and stop the service or package that may cause high volume utilization.
Note: this solution is from DSM KB guidance and may depend on DSM version.
Sources used: [9]