saveResource(string $name) not working as Expected

Always when I use this function, I have a folder right in the place where plugin.yml is at called "resources". I have also subfolders in it, I just do that "subfolder/fname.ftype". The file is saving but the returned boolean is always false and the file is empty but some are not. Default config for e.g is empty…

EDIT: Used files are .json files. But path is absolutelty correct. I even looped getResources() and did saveResource in that way. No chance.

 

PHP:

public const DEFAULT_PRESET_CONFIGS = array("config.json", "language/en_US.json", "language/de_DE.json", "language/en_UK.json", "EXECUTION_VALUES.json");

foreach(self::DEFAULT_PRESET_CONFIGS as $name) {
            $this->plugin->saveResource($name);
            StaticLogger::dev_info("Saving resource $name");
            $this->configs[$name] = new Config($this->plugin->getDataFolder() . $name, Config::DETECT);
        }

The code which gets executed