@elmo – thanks for sharing your backup – I was able to reproduce your issue on my machine 🙂
I have found one thing – missing content-type header (I have found it mentioned in Netlify documentation). After that sync started to working again 🙂
https://github.com/GetPublii/Publii/issues/732
I will make this fix available in the upcoming v.0.36.1 on the next week 🙂
I do hope that it was a reason, and as you can see – the error message is strange and totally not connected with the real reason of the issue.
