Crazy audio problem - mic cuts out after a few seconds in Discord/Google Meet

So this is probably the most insane problem I've ever had. The other day I joined my normal Discord server in the evening (using the desktop app) and tried to talk. People could hear the first 1-2 seconds of what I said and then nothing for 10 seconds or so, and then this repeated. No amount of adjusting audio settings made any difference. Meetings using Google Meet (run via Chrome) also have the exact same problem. The Windows 10 voice recorder app has no problems recording continuously, neither does Google Meet or Discord in Firefox. Audacity can also record fine. I find it interesting that both Chrome and Discord are Chromium-based - is it possible that Chromium does something different/special when it comes to recording audio?

I have 2 mics, a standalone USB one and a Jabra USB headset that I use for work calls - both experience the same symptoms. Both work fine on another computer.

Thinking that it might be USB related I bought a crappy 3.5mm mic - exactly the same issue. I even installed a fresh copy of Windows onto a spare SSD and everything is the same there, so I'm thinking this has to be a hardware problem at this point.

I'm using a fully updated Windows 10, Ryzen 3700X, MSI X570-A Pro, 2x8GB DDR4 3200MHz (XMP enabled in BIOS) and GTX 1660. Flashed the latest BIOS for the board as well, made no difference. It's worth mentioning that this hardware is fairly new - I rebuilt my PC in April - but it's all been working fine since then. I hadn't changed anything before it stopped working properly. I had a work call that morning which was fine, but by the evening when I tried Discord it was busted.

I'm going to try booting from a Ubuntu live USB and seeing what happens there, but given that non-Chromium apps on Windows work OK I think it'll be fine.

Has anyone ever seen anything like this before?