Due to the function of the AirVisual air monitor's PM2.5 sensor, to constantly pull air and particulates through its sensor chamber, sometimes it is possible that a large particle, such as a piece of dust or similar, may enter the sensor chamber, and get stuck there. This can result in a very high AQI number (e.g. AQI 1358) being displayed.
Fortunately, this problem is straightforward to fix.
To dislodge the particle, you simply need a can of compressed air, with a small spray valve.
You can then direct the compressed air toward the PM2.5 sensor, and spray for a couple of seconds. You can access the PM2.5 sensor through the little gap in the middle hollow of the monitor, on the device's front side.
You should see your monitor's readings return to normal, once the particle is dislodged.
See below image for reference: