Issue with wifi and Aluminium case

Hello all,
I have been using a RPi4 with Octoprint to control my 3d printer. Has been working fine for several months.
I have now installed the Aluminium heatsink case from Pirimoni, and since then, I have barely been able to connect to Octoprint, or the pi via wifi. The strange thing is, the issue only occurs when the printer is plugged into the pi. Basically, starting up the printer and pi, the Pi doesnt show up on the wifi network.
Starting up the pi only, it does show up.
Connecting the printer after the pi is working, normally drops the wifi connection.

But in summary, all these issues go away when I remove the Pirimoni Heatsink case.

Anyone else has similar issues, and have a resolution?

I have the red version of this,
Aluminium Heatsink Case for Raspberry Pi 4 – Pimoroni
WIFI is working fine as far as I know. I might have a small reduction in signal but it still works OK. I’m not losing my connection.