HDMI external monitor not working anymore

I have an external monitor at the office, that I plug on the HDMI port of my Macbook Pro (early 2015). It used to work fine before I was confined home back in March. Now that I'm back at the office, it's not working anymore: when I plug in the screen, it's just not detected.

However, displaypolicyd spikes my CPU and my macbook pro becomes really slow for a while. It actually worked once, but I'm not sure why. I tried under a guest user account, but it's the same, which have me thinking it's not due to a third party software.

Can it has something to do with an iOS update I installed since March? I use Catalina 10.15.5.