The most important question you must ask during an interview. How fast can a new developer become productive and start checking-in code? Is it days, weeks, months or years? Things that makes it difficult to start contributing in a new job are:
1. Legacy code base with no tests or documentation. Monolithic app.
2. No sharing of knowledge between developers in the existing code base.
3. Super star coders who dominate in pair programming and monopolize the keyboard.
4. Arguing about design ideas, instead of considering the design ideas based on its merit.
5. Allocation of work that does not take the strength of the developer into consideration.
6. Lack of requirements. No well defined requirements to start development.
7. Company got acquired. Original developers no longer with the new company.
8. Lack of product specific training.
9. Lack of domain knowledge.
10. Manager not resolving productivity issues faced by new developer.
11. Existing development team sabotages the work of new developer.
12. Difficulty in communicating with developers in different locations.
These things are based on my real world experience.