It could be a faulty sensor or even a software mis-match. I’ve heard of it before. As you’ve given the deep clean a try, I recommend resetting it back to factory settings, connecting it to the WiFi network/Dyson App and seeing if there a software update pending. Failing that, exchange it with Dyson. 

These two posts should see you right 

'Power Cycling/Restarting/Resetting' the air treatment machine | Dyson Community

Viewing your air treatment machine's software information | Dyson Community

Hi. I’d recommend installing the App. It send notifications when there’s an error identified. I received one when my unit failed to install a software update. Although the instructions where to reset the unit. 

Hi @Jessica3, 

It looks like you’ve had some great advice already - If this should fail to resolve the problem, I’d suggest speaking to the local Dyson team.

The easiest way to do this is to get in touch via our WhatsApp channel, where one of the team will be happy to discuss the next steps. To get started, simply click on our Guides and manuals link, navigate to the ‘Contact us’ section of the page and select ‘Start a WhatsApp conversation’. 

If you'd prefer, you're welcome to call the Dyson Helpline to speak with our experts directly. You can find their number in the ‘Contact us’ section of the page. 

Thanks, 

Stuart