Thank you for letting me know you have all displays working as expected.
There is something definitely wrong with the Plugable’s DP for this monitor. Fully tested. HDMI works where DP doesn’t. Not recognized in any form. Displaylink Manager v1.3 is what I’ve always used. The “1.3” should be the version number, as that’s what’s representing the Build.
Just to confirm, this statement is referring to the Asus PB278 not detecting a signal when connected to the docking station with a DisplayPort to DisplayPort cable?
I would be happy to help troubleshoot this monitor to see if we can get it working with the docking station’s DisplayPort output.
I recommend starting by connecting the DisplayPort cable from the docking station to the display, and disconnecting the HDMI cable from the back of this monitor.
Then use the manual input selection button ( 4th from the right on the LCD bezel, #4 in the image below ) to manually select the DisplayPort input.
This will help to rule out that the monitor is simply not automatically detecting the connected DisplayPort input.
I now have three displays displaying properly at full resolution. After posting this I will restart this evening to see if the new OS picks up on the Plugable off a reboot.
Please let me know if the update to macOS 11.3 helps to resolve the USB detection on restart issue, unfortunately we have had previous reports from users with 11.3 Beta that the issue was still present.