I got a reply to the support request, but it didn’t mention the invalid yml:
Hi Neil,
Thank you for contacting Transifex support and submitting your request.
Regarding your case, I would like to inform you that we have recently changed the way that this mode works since our scope was to keep the downloaded translation file as close to original as possible.
So, since this actually was requested by a lot of users, after further consideration we decided to proceed with the above changes.
Please accept our apologies for breaking your workflow and for any inconvenience that this may have caused you.
We hope for your understanding in this matter.
Regards,
Nina
That’s a big change that I couldn’t find announced or documented anywhere. But it doesn’t help if the yml is invalid.