with upgraded installations (from OJS2) some block plugins that were used in OJS2 had context set to 2 depending on the sidebar they were activated in. Now that there is only one sidebar in OJS3 the only value context can have is 1 but the upgrade script did not consider this. So if that is an upgraded installation, I would check the plugin_settings table for those values.
This is probably something worth taking into consideration in the upgrade script as well.