Dell D6000 wrongly identifies monitor as 'HDMI to VGA'

[accb]

Hi folks,
I've just joined and haven't found any threads that discuss this.
I have just replaced a D3000 dock with a (slightly) newer D6000.
The D3000 only had 1 HDMI and a DVI port.
The D6000 has 1 HDMI and 2 DP.
I have 2 identical BENQ GW2280 monitors. These have HDMI and VGA inputs.
I previously attached one monitor with a DVI-DVI cable with a DVI-VGA adapter. (The other was HDMI-HDMI.)
I am nnow connecting both monitors with DP-HDMI adapters and HDMI cables.
One monitor is detected as "BenQ GW2280" and behaves perfectly normally. But the one that used to be connected with the DVI-VGA adapter is detected by Displaylink as "HDMI to VGA" and does not offer the same resolution options.
Also - the BENQ menu is unavailable, only allowing selection of inputs.
I've tested the monitor with a different computer and direct HDMI-HDMI connection and it works correctly.
I've tried cleaning out the Dispaylink software from the computer, and rebooting. I've tried different cables and ports (the momitor has 2 HDMI). I've tried using the D6000 HDMI port instead of the DP.
Any suggestions welcome.