For years I've been using a Dell U2515H monitor as external display for my Macbook Pro. Yesterday I purchased a second monitor (exactly the same) and connected it through HDMI to my Macbook Pro (2018) using a docking station. The first monitor is connected over DP.

The screen is working, but my Macbook doesnt recognize it as a second monitor, it just sees the Macbook and one external screen (Dell U2515H) in Display settings.

I have tried to hold down the option key to use the 'Detect displays' function, but that doesnt do anything.

I have no other screen around to test on to see if this is an issue because the two external monitors are exactly the same model.

2 Answers 2


I was using the Hyperdrive Pro Docking Station, and apparently its sharing the signal for its HDMI and DP port. I had to buy an adaptar (USB-C to HDMI) to attach the second monitor to the hub, and this solved the issue.


The mac support: https://support.apple.com/guide/mac-help/use-multiple-displays-mchl7c7ebe08/mac

It says

For Mac computers with Thunderbolt 3 (USB-C): You can connect a single display to each port. If you connect multiple Thunderbolt devices to each other, the Thunderbolt 3 display must be the last device in the chain. If your Thunderbolt 3 display has USB ports, those can be used for data and power.

So, I am connecting it to another USB-C port of mac. I am not sure if this is the best way, but Mac is limited to support this..

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