How to reset plugins cache in JIRA - Tempo Gadgets not loading

How can I clear the plugins cache in JIRA?
After updates, it can happen that Jira is trying to load outdated information for plugins. This can cause problems when loading plugin information, most commonly it affects the Dashboard gadgets. 
This can be fixed by clearing the Jira plugin cache, to make sure that actual, not cached plugin data is used when loading views.

To delete/clear the JIRA plugin cache if you get random plugin behavior:

1. Stop the JIRA instance

2. Delete JIRA_HOME/plugins/.bundled-plugins and JIRA_HOME/plugins/.osgi-plugins ( just these two folders!)

3. Restart JIRA