[fix][ui] using the sleep function wrongly within the Qt threads

CHANGELOG.md

@@ -42,6 +42,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
     - not calling initial required tasks after enabling a new package type on settings
     - not updating the type filters if only one type is available after refreshing the table
     - displaying the type filters on the search results when there is only one type available after some actions finish
+    - using the sleep function wrongly within the Qt threads (causes random crashes)
     - minor fixes
 - Tray
     - update notifications not working on Ubuntu 18.04