Due to the way plugins are loaded by Redmine the variable

ActiveSupport::Dependencies.autoload_paths 

contains the path to the 'lib' directory of each plugin twice, which should not happen.

When Redmine loads the plugins from @config/initializers/30-redmine.rb@ it calls

Redmine::Plugin.load

@Redmine::Plugin.load@ (defined in @lib/redmine/plugin.rb@) adds the 'lib' directory of each plugin to

ActiveSupport::Dependencies.autoload_paths 

and to

$LOAD_PATH #alias $: 

When each plugin calls

Redmine::Plugin.register 

from init.rb (which they ought to do), then in @Redmine::Plugin.register@ all Rails paths in the plugin directory are created by calling

engine_cfg.paths 

implicitly by calling

engine_cfg.paths.add 'lib', eager_load: true

Then in @Redmine::Plugin.register@ the following call causes the second addition of the autoload_paths

ActiveSupport::Dependencies.autoload_paths +=

        engine_cfg.eager_load_paths + engine_cfg.autoload_once_paths + engine_cfg.autoload_paths

In some environments this may cause trouble.