The following guide will teach you how to solve the database Mysql2 table already exists error. It is a serious problem as Redmine crashes in general and could be related to any of our plugins.
If the problem appears at your Redmine, then the error logs (in the production.log file) should look like this:
Mysql2::Error: Table 'name_of_the_table' already exists: CREATE TABLE name_of_the_table
Note: The name_of_the_table depends on which plugin the error is appearing on.
The error itself means that the migration was broken some time ago. Please follow these steps to fix it: