Ian,
I tried a few things that made it work, although inconsistently.
1 – Events > Settings – Turn off the set WooCommerce trying to complete orders automatically option
2 – I had custom code in my functions.php that was attempting to do the same thing ie. auto-complete the woocommerce orders. I commented that out
3 – if your gateway was using an iframe to process payments on the page, try switching to a redirect to the payment gateways servers instead
This has seemed to work for most users, but I don’t think its back to normal just as yet.
Hope this helps.
Guha