It should loop. Freezing on the last frame was a bug in versions before 3 and is fixed, so first make sure the plugin is up to date. If it still happens, the clip is probably an HEVC or ProRes file whose length the renderer cannot read: export it as an H.264 MP4 and attach that. If that does not help, send the clip to info@videoexportify.com.
Try it on your own frame
Free to try, no account. Or watch the plugin work in the browser first.