Sometimes, it may be the case that your Node/Pro's screen may update its readings at a slightly different rate than to your AirVisual app.
Your device will take measurements at different intervals, depending on its sensor mode. See more about the different sensor modes here:
In the standard 'Default' sensor mode, the Node/Pro will take a measurement every 5 seconds when actively being used (this means when buttons are being pressed). After 10 minutes of inactivity, when the screen is still on, the Node/Pro will change to take measurements every 5 minutes. Meanwhile, at any time when the screen is off, the Node/Pro will take measurements every 15 minutes. These new measurements will be displayed on-screen, whenever the Node/Pro's screen is on.
If the device is connected to internet, its readings will update on the app once every 5 minutes. What is then displayed on the app is shown as the average value for the past 5 minutes. Therefore, if your monitor screen is showing updated measurements every 5-10 seconds, but your app does not reflect these immediately, this is the reason why.