@ManSurfingOnLifeBuoy

On the Dell D6000, the third monitor on HDMI is never driven by DisplayLink technology. Only the first two are (whatever the port used: 2xDP or 1xDP+1xHDMI) but in 2 monitor configuration the DL chip/driver only drive the 2xDP ports.
Therefore changing DisplayLink driver won't really do much. It might temporarily look like it worked if the port eventually negotiated DisplayPort properly, but I would call that a coincidence.

This sounds like an Alternate Mode issue. You could try the different D6000 firmware from Dell website which would update the integrated DisplayPort to HDMI chip behind the HDMI socket.

Regards,
Alban