I can set the default when entering the watch page/fullscreen and zoom in/out according to the desired value. But I think that's what you really want. To make the subtitles appear, try using my extension called "Youtube Subtitle Position" first. It can move the subtitle position and has an option to remember that value. If it really doesn't work, send request via "issue/suggest" button on the options page and attach a link to the screenshot of the missing subtitle. I think it's strange that the subtitles are missing.