uninitialized constant ActiveStorage::Analyzer::ImageAnalyzer::MiniMagick

I'm getting this error on a Rails app on Heroku:

NameError: uninitialized constant ActiveStorage::Analyzer::ImageAnalyzer::MiniMagick
/app/vendor/bundle/ruby/3.0.0/gems/activestorage-6.1.3/lib/active_storage/analyzer/image_analyzer.rb:46:in `rescue in read_image'

It's happening in Sidekiq jobs generated from ActiveStorage::AnalyzeJob and seems to trigger whenever I try to upload an image to my AWS storage (the images are not reaching my bucket).

What is odd is I have a duplicate staging version of the app on Heroku that uses the same config and it does not trigger these errors (the images do reach my bucket from staging).

Both versions of the app are using the same gems and buildpacks.
Both versions have ImageMagick 6.9.10-23 and mini_magick 4.11.0 installed.
And both versions show the same error at the console if I reference the class mentioned, e.g.:

$ heroku run rails c -a my-staging-app
Running rails c on ⬢ my-staging-app... up, run.9122 (Free)
Loading staging environment (Rails 6.1.3)
irb(main):001:0*  ActiveStorage::Analyzer::ImageAnalyzer
=> ActiveStorage::Analyzer::ImageAnalyzer
irb(main):002:0>  ActiveStorage::Analyzer::ImageAnalyzer::MiniMagick
Traceback (most recent call last):
        1: from (irb):2:in `<main>'
NameError (uninitialized constant ActiveStorage::Analyzer::ImageAnalyzer::MiniMagick)
Did you mean?  MiniMime

But I have no idea why the staging app doesn't hit the error when uploading to AWS.

Does anyone know how I can fix the uninitialized constant? (Where does the referenced class need to come from?)