The existence of the reloadPlugins.groovy plugin in the plugins dir causes Artifactory to reload all the plugins in an endless loop. The reason being the reloadPlugins.groovy file is never actually loaded due to a deliberate check in the code on versions 5.x. This causes the actual list of loaded scripts to always have a different size than the list of plugins in the 'plugins' dir, tricking artifactory to think it should reload the plugins every time the ScriptReloader thread wakes up.
Except being an annoyance, some plugins can behave really badly if they are reloaded repeatedly. This should be handled with high priority..
The overall problem is not just the reloadPlugins plugin, the same situation would happen if a plugin (any plugin) fails to load and the groovy file is kept in the plugins dir.