In newer Ruby (2.4.6) and Redmine (3.4.10) versions Redmine settings are not handled as HashWithIndifferentAccess, so using symbols for setting keys do not work anymore. You can try the behavior by going to Redmine Admin plugin settings page and try to change plugin settings, you will notice saving the settings will not work. These changes should fix that.
In newer Ruby (2.4.6) and Redmine (3.4.10) versions Redmine settings are not handled as HashWithIndifferentAccess, so using symbols for setting keys do not work anymore. You can try the behavior by going to Redmine Admin plugin settings page and try to change plugin settings, you will notice saving the settings will not work. These changes should fix that.