It was mentioned somewhere in one of the recent threads on OS 3 that WD did away with the WebDAV code on the web portal (formerly WD2Go.com now MyCloud.com). Unless one upgrades their device firmware and the associated WD remote apps/software, its shouldn’t be a surprise that the web portal at the very least no longer works properly or at all with older firmware that still relies on WebDAV for remote access.
As such people are faced with a trade off, use the older firmware and have potential trouble with remote access, or upgrade to the OS 3 version firmware and loose the features or modules they had installed on the older firmware but gain remote access.
Edit to add: Here is a post where it is explained why WD dropped using WebDAV and is now using Webfiles for the remote portal.
https://community.wd.com/t/wd-my-cloud-mac-only-uploads-512-kb-and-then-stops/96465/73
