Resolving common issues

Most issues come from conflicting versions: having more than one app and Quicklook/macOS not choosing the latest one.
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The latest version can be distinguished because there is a visual difference in the Finder panel between the latest stable version and other version:
1. do you see a Finder panel preview with the 'round' play icon and with no scrollbars like in this screenshot?

2. I assume you don't, if you can please open spotlight cmd + space and type webm to see if there is more than one 'Webm Quicklook? Please scroll down complety the spotlight, sometime it hides down. In my screenshot here, I have two, however I know which one is linked and that is the one in /Applications

3. I assume you do have more than one 'Webm Quicklook' app:use the arrow keys to select/highlight the first app in the spotlight, then press space to have it Quick Look (need use arrow keys first) and see if they all have Version: 1.62 like in the screenshot

4. I assume one has something else than Version: 1.62, move with arrow keys to select/highlight it, then press cmd + return in order to open its location: that is where you need to move the latest version so to replace the older one, then relaunch it just to be sure.