I've tried both v2 and v3, in my own app and in the Try this API and Playground.
In all cases, I receive a 200 OK response with an empty response body. Exporting to application/pdf does seem to work.
I've been in contact with G Suite support. They're taking it very seriously, but they are suggesting that this is a localized problem.
As it's happening for my on both business and personal accounts and also for colleagues, I'm wondering if the problem is more wide-spread.
Thanks in advance!