MacBook Pro suddenly doesn't support 2560x1440 external monitor

There was some security update from Apple on 17 January, and the following day I couldn't get the resolution right.

There was no mDP signal from my device, whether I used an thuderbolt to thunderbolt cable (as always), or DP to mDP cable. There was just no signal at all.

The monitor now only connects with an HDMI cable that does support 4K resolution, but the macbook settings allow only much smaller resolution now.

How can this be sorted?

Thinking that the cable was the issue I spent almost £40 on a new cable from Apple and another one HDMI for £15.

Not cool...

Thanks!