This definitely is not typical just because of a DND sign.

Trying to get an idea of when/why they suddenly would have you/your room under the proverbial microscope at night. What kind of room rate did you have for the stay and were there any issues about payment at any point during the stay?

How much time was there between when you last entered the hotel lobby, last opened your hotel room door, and the hotel ringing the room phone?

Sounds to me like they seemed extra eager to get a peak into what was going on in the room and were probably trying to provoke you into giving them additional excuse to check out the room or you closer, otherwise bother you, or even shopping for excuses to boot you from the property. Sorry to hear they hassled you, but unfortunately it doesn’t surprise me that it happens to some. Hopefully the hotel gives you some kind of explanation for why this hits you at 10:30pm and then you can decide on what to do from there. This is unlikely to have hit you this late in the evening just because of a DND sign still up, so hopefully you find out more about why it happened like this.

Personally, if two people come to my hotel room door at that time without me expecting them, I would be reluctant to open the door and would even consider calling 112 to get the police to check out the hotel employees/security contractors if my call down to the front desk didn’t first confirm that the hotel had sent them to my room and the purpose. And I would have already fed and be feeding the data about what was going on to someone offsite to make sure there is a trail to follow in case things go more seriously wrong upon the door being opened. With or without a key card being needed to use the elevator to get up to the rooms, questionable characters — uniformed or not — can still get onto the room floors.