Display problem with docking station with two monitors

I have Ubuntu Mate 18.04.2 installed on my dell laptop. The laptop is on a docking station with two 24" Samsung monitors connected (one 1920x1080 and the other 1920x1200). Via Display, I have switched the laptop screen off and the two external monitors on.

The problem is that the 1920x1200 monitor blinks incessantly. On, off, on, off, etc.

Any idea what the problem might be and how to fix it? Naturally I'd be happy to provide more info.