Image Upload Issue: Class "WebPConvert\...\Stack" not found

This is a new one for me: I’ve updated a Kirby instance on a server from 3.6 to 3.7, replaced the webp plugin with Kirby’s native webp conversion, upgraded everything to PHP 8.1 and set the server to PHP 8.1 FPM.

Now I’m getting this error on trying to upload an image in the panel. I can’t really tell which of those steps made this happen. I don’t find a dependency like that in the composer.lock file. I already removed the panel to let it update. Bit lost here, but also can’t think of this being a big issue. I just don’t know whether this is a server issue or an issue of my Kirby instance.

Screenshot from 2022-09-06 17-50-25

The error message points to this dependency “rosell-dk/webp-convert”: “^2.4”. My guess is that you haven’t completely removed the old converter stuff, so that it’s still called somewhere?

You were right. Silly me. My script for uploading changes to the server doesn’t remove folders. Even thought the composer dependencies were cleaned, the folder of the plugin under plugins was still there. I often forget that is not all coming from the vendor folder.

Thank you. It probably wouldn’t have crossed my mind.