Thank you for taking care of the initial troubleshooting, and for sharing your observations here. While it does look like you have covered all bases, can you confirm that you have followed the process in the steps below? I have copied it from this document Error trying to use Share Online feature
If you have and you are still facing this issue, I suggest reaching out to us directly using this link Contact Customer Care
Error code 44
Error code 44 indicates that XD was unable to upload your content to Adobe Creative Cloud. This could be the result of a service issue on the Adobe side, or a network connection issue on your local machine. If you receive error code 44, trying the following steps to identify the root cause and resolve the issue:
Switch to a public network and try to share a simple file that contains only one artboard. If sharing works from a public network but not from an enterprise or other managed network, the issue may be related to your local network settings.
XD needs to access different Adobe domains to publish content to Creative Cloud. If access to any of these domains is blocked, you receive error code 44. See Adobe Creative Cloud Network Endpoints for more information on which specific domains need to be whitelisted.
If sharing a small file works, but you receive an error when attempting to share a large file, the issue may be related to the stability of your local network connection. Try sharing from another network, and if possible, use a hard-wired connection.