Reinstall app & check Wi-Fi
Remove the Dyson Link app from your device and re-install the latest version from the app store.
Check the following:
Is Wi-Fi privacy 'enabled'?
This stops devices talking to each other – you will need to disable WiFi privacy for the purifier to connect.
Are parental controls enabled?
Temporarily disable any parental control settings whilst setting up the purifier on the network.
Re-program the instruction (e.g. schedule) to test the machine.