I was playing with Google's AI thingy and came across this. Seems to be regular offer on this route which is kinda of intermittent throughout the week.
Return in the example is a long layover. Maybe someone can make something out of it. You can get the above price through flightoffice.co.uk (never heard of them) or directly with Hainan for 1770e.

https://www.google.com/travel/flight...sas=1&curr=EUR