I am using a Dell Latitude 5420 laptop which works fine with other monitors but on this AIO it won't go above 1360x768 - makes it unusable for me to switch between personal (AIO) and work (laptop). 

All drivers are up to date as far as I can tell

The All-In-One runs fine at 1920*1080 natively so the panel can certainly run at that resolution

The Laptop outputs at 1920*1080 to another (dumb) screen

The All-In-One displays input from my Linux machine at 1920*1080 through the HDMI-in port

It's just the combination of HDMI-in into the All-In-One from the Latitude 5420 that doesn't work

For the record, it's a simple HDMI cable, no adapters or converters involved

Any help gratefully received!