Steps to reproduce:
Make an api call with action=visualeditor&paction=parsedoc for any page:
https://simple.wikipedia.org/w/api.php?action=visualeditor&paction=parsedoc&page=Wikipedia:Sandbox resulted in:
{ "error": { "code": "internal_api_error_TypeError", "info": "[8951fed5-732f-4380-9b31-e5d5a3886ca2] Caught exception of type TypeError", "errorclass": "TypeError" }, "servedby": "mw1396" }
https://en.wikipedia.org/w/api.php?action=visualeditor&paction=parsedoc&page=Wikipedia:Teahouse resulted in:
{ "error": { "code": "internal_api_error_TypeError", "info": "[a5805455-8fbf-4944-8c43-4ec817155eca] Caught exception of type TypeError", "errorclass": "TypeError" }, "servedby": "mw1283" }
There are also errors for using paction=parsefragment for the same pages