Suggestions for placement of ST Multipurpose Sensor on door

The iris sensor is typically one of the quickest to respond, so I would look into two possibilities.

First, the placement of the sensor itself. See the following FAQ:

Second, if sensor placement doesn’t solve it, then consider the “strength of your mesh,” which means how many mains powered devices you have and their placement to help pass the signal along to your hub. Battery powered devices cannot help in this regard.

See the following thread. Start with post 11, then go back up to the top of that thread and read the whole thing. (This is a clickable link)