App 8596 output: Error: The application encountered the following error: uninitialized constant Mysq

Getting this error using ruby 2.6, rails 5.0 and mysql2 0.5.2
Same error if I use ruby 2.3.3

The bundle completes without errors whether I use ruby 2.3.3 or 2.6.0

Assuming you read the Ask Smart Questions article you were pointed to, and thus used copy and paste to get the exact error message, then it looks like you left an L off the end of the word MySQL. What does a grep of your application turn up?