(FWIW, WFM with citoid here https://test2.wikipedia.org/w/index.php?title=Sandbox&type=revision&diff=317924&oldid=317458 - but I swear I had done that same edits a few seconds before - I was sure I had saved it correctly...)

Yes, that error does not effect adding the citation and saving it correctly. The error appearing in the console is a seemingly harmless regression nonetheless.

(Thanks for the clarification! In T166254 my console screamed at me as well, but the action is also failing there.)

Can't reproduce. Which page/browser?

Reproducible here with Chrome and Firefox: https://en.wikipedia.beta.wmflabs.org/wiki/User:RYasmeen_(WMF)/sandbox?veaction=edit&section=1

I haven't been able to reproduce this either, Chrome or Firefox. More detailed reproduction steps? (I also don't get that missing/empty |title error you have, also using bbc.co.uk, which may be related.)

I can reproduce this... but only on the specific page that @Ryasmeen linked in her example.

1. Go to https://en.wikipedia.beta.wmflabs.org/wiki/User:RYasmeen_(WMF)/sandbox?veaction=edit&section=1
2. Edit page in VE
3. Click "Cite"
4. Type "bbc.co.uk" into box and click "Generate"
5. Reference is shown, click insert

The reference is successfully inserted, but the error is shown in the console.

Yeah not sure what's special about that page that would cause this. I am being able to consistently reproduce it, even if I blank the whole page and then add citation :(

Oh hey, I think this is T168932 as well. (Same error, at least.)