After upgrading to the latest Zotero, I succeeded once when adding citations. Then, the issue starts again.

Method document/execCommand failed at chrome-extension://ekhagklcjbdpajgpjgmbionohlpdbjgc/connector.js:309

The same as the original thread: When I clicked "add citations", I was able to properly add citations as before just for once; then, I could still go through the same procedure, but no text was added to the document after the process plays out (the green progress bar shows and disappears).