I still have not received a stamp in my passport regarding the submission of the application. Is it a problem if I have to show my passport to the police and my visa has already expired?

Submission of the application in person preceded by registration of the visit in inPOL Foreigner Portal is the best way to get a stamp in your passport. If the application was sent by traditional mail, in order to meet the formal requirements and receive the stamp, you should wait for a letter/phone call from the local office. During the meeting with the police in the period between the expiry of the visa and the receipt of the stamp in the passport, you can provide, for example, the case number, the date of sending the application to the local office and what kind of application it was. The Police and Border Guard will be able to obtain confirmation of the information provided.