Ok, I've tested it with a VPN address in the US and it works so that appears to be the issue.
When the VPN is set to the US, I am able to send the full 1536-element vector array and successfully receive query results. When accessing from other countries (France, Singapore, UK and no VPN), no data /object is returned at all (it's blank), unless I reduce the array to 100 elements by splicing and then it returns data, albeit not useful as results are based on an incomplete vector array.
May this be a configuration issue on Cloudflare's side?