What wifi chip are you using? Debian by default has no unfree wifi drivers included, so that can cause issues with them. If you have a good wifi adapter by a vendor that pushes drivers upstream like Mediatek, it should work just fine out of the box.

or install from non-free ... which will not be needed anymore for next release

https://cdimage.debian.org/cdimage/unofficial/non-free/cd-in...

Yes I was using the non-free version. It was working fine until I'd set the machines to auto-update then one day found out they had zero connectivity after an update. I thought about going around to each machine and manually trying to revert back whatever was in the updates that broke it and just decided to wipe and install Ubuntu back on them.

Would using debian non free address this?

I presume so, but I wouldn't know because I haven't ever tried.

WiFi is working for me even if I mostly use the Ethernet card.

lshw tells me

  description: Wireless interface
  product: Centrino Advanced-N 6235
  vendor: Intel Corporation

I'm using the iwlwifi driver.