See reports here: https://en.wikipedia.org/wiki/Wikipedia:VisualEditor/Feedback#HTTP_503_errors
- Repeat the steps, but after you open the save dialog, dump the HTML output (how to here: https://www.mediawiki.org/wiki/Parsoid/Debugging#Dumping_HTML_DOM_before_save_in_VE)
- This HTML crashes the currently deployed version of Parsoid.
- You will notice that the issn parameter for the transclusion has {"wt": [...]} instead of {"wt": ".."} .. i.e. Parsoid is receiving an array containing a string instead of a string for the wt parameter.
https://gerrit.wikimedia.org/r/#/c/192349/ is a fix in Parsoid so the serializer doesn't crash if a non-string parameter is passed in (it also logs an error event), but this should be fixed in citoid/VE. We'll try to get this fix deployed to Parsoid as part of the regularly scheduled Parsoid deploy for this afternoon.