Unknown "(technical) review", lack of communication
After more than a year of using N26 as a wallet (not for serious banking), without any specific activity like receiving or sending a considerable amount of money, I received an email notification that my account is under "(technical) review" and freezed until an unknown date that the review is finished!
The interesting point is that in the email they explicitly mentioned "refrain" from contacting the support!

(Edit: the account is now unfreezed after 8 days without any communication. I realized it by chance.)

I don't know what was the issue, maybe they wanted to check my supermarket purchases! 
Fortunately, I barely transferred / saved more than 100Euros to / in my account and had less than 70Euros blocked. But, what if I was receiving my salary in my N26 account or paying my bills and rent through it?
They could've at least called me or sent me an email to explain the issue. I will never trust this bank as an option to deposit a considerable amount of money.