If you look in your Documents>Zoom folder (or wherever you've chosen to store Zoom recordings), do you have files that say something like "double-click-to-convert"? If so, try double-clicking on the first one of these (normally there are two). That should get it to start converting.
If you can't still find it, I would suggest that you log a problem with Zoom Support at
https://support.zoom.us/hc/en-us/requests/new
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