Why does my phone keep disconnecting from wifi?

A

AC Question

Phone keeps disconnecting from wifi

I have a Doogee x5.It keeps losing wifi and wont connect back until I reset the router .Sometimes it will connect for a few hours before disconnecting .The message I get when trying to reconnect is "authentication problem" .I am on Virgin Media broadband.
I'm a bit of a technophobe so any help will be gratefully received.
Thanks