[QUESTION] surgery randomly impossible

I've posted this problem a while ago on the steam board, but as I got distracted from the game couldn't get a closer look. Came back now with a new game and it happened again, and this time I managed to get a savegame.

Description
Sometimes surgeries are not possible for specific patients. I have sufficient staff and rooms, and surgeries work perfectly fine 24/7 (as a matter of fact, a surgery even took place when I saved). But suddenly I get the notification that a certain patient can't get treated and the icon is greyed out.
If I move the patient to ICU however, the icon gets selectable once the transportation job starts. (And the surgery will be performed evetnually).
This happens once in a while, and still feels completely random.

This patient must be hospitalised at HDU/'Einweisung Überwachungsstation" or "Einweisung ITS" for surgery to occur. This patient is currently in regular hospitalisation/Stationäre Aufnahme. You need more Einweisung Überwachungsstation beds. If you hover over a treatment or examination that is not available, a little information card will pop up, explaining why it's not available.