Doing a migration we ended up in a crash that was hard to understand.

In 2.5.x LTS EE, we have a project with many content types in many Content Type Groups. I don't know how they did this but they did (prob legacy).

This situation is working well in 2.5 but in 3.x it is crashing the admin.

Reproduction steps:

• Add in the database table `ezcontentclassgroup_classgroup` a record to define a Content Type in 2 Content Type Groups. 
• Clean redis
• Reload the admin

You will see:

An exception has been thrown during the rendering of a template ("Field "folder" has already been rendered, save the result of previous render call to a variable and output that instead."). 

Thanks