Getting "uninitialized constant ActsAsTaggableOn::Taggable::TagListType"

[amree]

I tried to upgrade from v6.0.0 to v6.5.0, but somehow I got this error in Production (not my local):

uninitialized constant ActsAsTaggableOn::Taggable::TagListType Did you mean? ActsAsTaggableOn::TagList

The error stack shows that it's happening on Rails.cache.fetch line which I think is pretty random. It's not like the code block is calling the tag list. It is a weird error as if it tried to run the new code, but it is not there.

Any pointers so that I can investigate what could go wrong would be great.

I'm using Rails v5.2.7 and Ruby v2.5.8