Well that shows it IS finding lots of matching images, cataloging them, and caching them.
alfred: ScriptFilterResponse(items: [Alfred.ScriptFilterResponse.Item(arg: "dummy", uid: nil, title: "Select with arrow keys, drag-n-drop with mouse", subtitle: Optional("[↩: search again] [⌘: copy GIF] [⌥: copy URL]"), valid: nil, match: nil, autocomplete: nil, quicklookurl: nil, type: nil, text: nil, icon: nil, mods: nil)])
2021-05-28 13:30:12.264 AlfredGifBrowser[7397:4565081] [WebViewCache.swift:79 startCacheDirWatcher()] Adding to cache due to FS change: 1B76D167EC3A8E056B9CE1040662B00BE99E1229)
2021-05-28 13:30:12.264 AlfredGifBrowser[7397:4565081] [WebViewCache.swift:38 addToDict(recordFileURL:)] Web URL in cache: https://c.tenor.com/7I9nkd071vYAAAAM/food-coma-food.gif
2021-05-28 13:30:12.264 AlfredGifBrowser[7397:4565081] [WebViewCache.swift:44 addToDict(recordFileURL:)] Cache dict size: 385
Lots more results like these (after the line that sets the Alfred response), but no error or indication of why the view itself isn't showing.