ATEM audio suddenly stopped recording clean audio

First time posting a question here so apologies if details are missing and are unclear, I shall do my best to make everything make sense.

So at the studio that I'm currently working at (it's for a couple of YouTube channels) they've been recording audio through an ATEM Mini Extreme ISO. Prior to my starting there, they were using these older Canon/Sony Camcorders and feeding the video feeds through a Feelworld Monitor. They had recently bought a batch of BMPCC 6K cameras that replaced all of the camcorders, still feeding through HDMI hookups (yes I know we should be using SDI inputs, but it's all a work in progress right now). And this is where issues started happening; So the audio is being captured through a set of Shure microphones, that are feeding into a Focusrite mixer (not sure of the exact model, sorry I will have to double check) and then being fed through an AUX port directly into the ATEM mic line.
The audio was very clean, no noise and no issues, and then one day one set suddenly started getting massive electrical buzzing through the miclines. I cleaned the ports and connections, and recently purchased a ground isolater and hopefully that will fix that particular issue. But on the other set, the mics now peak and distort like crazy and this all happened out of nowhere. The only things that have been replaced are the cameras, nothing on the audio end was really changed.

Worth mentioning, when the audio is recorded through Logic or Audition, it's perfectly clean. No distortion, no peaking, nothing. It sounds great. It's only when plugged into the mic line on the ATEM that the audio completely trashes.

Any help would be appreciated.

Have you got the ATEM set to mic or line input?

Have you got the ATEM set to mic or line input?

So I've tested both, same results. The Line input is a LITTLE cleaner, but it's still present.

Can't see how changing the cameras would affect the audio. The obvious test would be to unplug all the cameras and check if the audio distortion is still there. Is the Focusrite mixer input to the ATEM from a balanced or unbalanced feed (Atem doesn't like balanced feeds)? Have you tried plugging one of the microphones directly into the Atem as a test (changing impedance to "mic")? Any new electrical appliances recently installed (fridges, MRI scanner, etc.)?
Have you tried changing the cables? If all checked then sounds like a fault on the Atem.