rails: Rails 6 app does not render templates when started from a Dropbox folder

Steps to reproduce

myuser@192 Dropbox % pwd
/Users/myuser/Dropbox
myuser@192 Dropbox % rails new bugreport
myuser@192 Dropbox % cd bugreport 
myuser@192 bugreport % bundle
myuser@192 bugreport % rails g controller testc index
myuser@192 bugreport % rails s

http://localhost:3000/ # Yay! You’re on Rails!

http://localhost:3000/testc/index 
# No template for interactive request
# TestcController#index is missing a template for request formats: text/html

Exit Server

myuser@192 bugreport % cd ..
myuser@192 Dropbox % mv bugreport ../
myuser@192 Dropbox % cd ../bugreport 
myuser@192 bugreport % pwd
/Users/myuser/bugreport
myuser@192 bugreport % rails s

http://localhost:3000/testc/index 
# Testc#index
# Find me in app/views/testc/index.html.erb

Expected behavior

The app should work independant from the folder it is started from. Just like it did in 5.2 which is not affected by this issue.

Actual behavior

Rendering any ERB view fails.

Log output:

`Completed 406 Not Acceptable in 5ms (ActiveRecord: 0.0ms | Allocations: 1970)
 
ActionController::MissingExactTemplate (TestcController#index is missing a template for request formats: text/html):`

System configuration

Rails version: 6

Ruby version: ruby 2.6.3p62 (2019-04-16 revision 67580) [universal.x86_64-darwin19]

Operating System Mac Os Catalina