Enable Performance Logging
In the Confluence Administration → Logging and Profiling section add a new Entry with Package
de.griffel.confluence.plugins.plantuml and Log Level
After that you should see the rendering performance for each plantuml macro in the
"Error: dot cannot generated PNG file. Check your dot installation.
Check your installation using PlantUML Version Information.
Ensure that the correct version of Graphviz will be used either by setting the environment variable
GRAPHVIZ_DOT or by adding dot to the search path.
German umlauts or other non ASCII characters are not shown correctly in generated graphs
This error is caused if two different versions of the plugin are installed in Confluence.
In newer Confluence versions (>= 7.10) this problem happens just by updating the plugin and could be solved by just restarting Confluence. If this does not help then please try to uninstall the plugin and then reinstall the plugin. If this does not help then perform the steps described here: https://confluence.atlassian.com/confkb/how-to-clear-confluence-plugins-cache-297664846.html