ActionController::UnknownFormat only on Heroku

Question

In the heroku logs I see the following.

app[web.1]: Started GET "/tags/1" ...
app[web.1]: Processing by TagsController#show as HTML
app[web.1]: Parameters: {"id"=>"1"}
app[web.1]: Tag Load (1.2ms) SELECT "tags".* FROM "tags" WHERE "tags"."id" = 1ドル LIMIT 2ドル [["id", 1], ["LIMIT", 1]]
app[web.1]: Completed 406 Not Acceptable in 7ms (ActiveRecord: 1.2ms)
app[web.1]: ActionController::UnknownFormat (TagsController#show is missing a template for this request format and variant.
app[web.1]: request.formats: ["text/html"]
app[web.1]: request.variant: []

In dev env the page is rendering fine and I don't see the error.

> ls app/views/tags
_form.html.haml new.html.haml show.html.haml

Controller

class TagsController < ApplicationController
 before_action :authenticate_user!, except: :show
 def show
 @tag = Tag.find(params[:id].to_i)
 end
 ...

• Pavan: What is request format coming to show action? Seems like it is not HTML.
• Jay-Ar Polidario: yeah, I'm guessing it's either a JSON or JS request
• James Klein: It is HTML. I added more of the log output in the question
• Pavan: Ok. It IS HTML. Also I can see you have show.html.haml. Can you confirm it again that show.html.haml is present inside the app/views/tags?
• James Klein: my global gitignore was ignoring the tags dir because that's the same dir name that vim uses for ctags. Error messages do not lie, the views weren't there. Thanks for the help