Mailboxes are missing for store manager or amb's

Summary

Mailboxes are missing for store manager aka biebs.

Steps to reproduce

Currently not reproducible. The cause is so far unclear.

What is the current bug behavior?

This will prevent the Biebs from creating business cards.

What is the expected correct behavior?

The mailbox should be usable.

Test people:

NO inbox

• 279535 (bieb quiz probably before oct 2019) a fs-friend of @jofranz (fixed) ✔️
• 319890 (bieb quiz ~14. september 2019. First clicked on the inbox late october 2019) a fs-friend of @jofranz (fixed) ✔️
• 253484 (support case) (fixed) ✔️
• 247974 (support case) (fixed) ✔️
• 190470 (support case) (fixed) ✔️
• 285809 (support case) (fixed) ✔️
• 320456 (support case) (fixed) ✔️
• 274993 (@koenvg)
• 316015 (support case) (fixed) ✔️
• 295531 (support case) (fixed) ✔️
• 337854 (support case) (fixed) ✔️
• 190971 (support case) (fixed) ✔️
• 245974 (@MarinaGeorg)
• 339586 (@JessiH ) (fixed) ✔️
• 236762 (support case) (fixed) ✔️

with inbox

• 301788 (bieb quiz late october 2019) via @Isabel_Bonn (this might be a name where there was no need to add a number at the end so first attempt of name creation was successful. There are only 1-2 persons not active with the same letter)

Relevant error messages and/or screenshots

• https://gitlab.com/foodsharing-dev/foodsharing-it-support/issues/636
• https://gitlab.com/foodsharing-dev/foodsharing-it-support/issues/233
• https://gitlab.com/foodsharing-dev/foodsharing-it-support/issues/389

User get a 500 (Internal Server Error) when they want to print a business card.

https://sentry.io/share/issue/5e1864c1fcfb4ec4a269dd6040aca4d7/

For the store managers that get the error, mailboxes are missing.