I have a simple Google Script published as a web app with anonymous access. The code is available here and the web app is available here.
code.gs
Yes it is consistently reproducible in a new project.
I have the same problem... It is related to the HtmlService
The app script was workng for about a year, but yesterday started to return the error "Google Docs encountered an error".
return HtmlService.createHtmlOutput("<p>Hello World</p>");
If I login it works, however the script is meant to return dynamic list as html when people visit my website, hence why it is needed to run as "as anyone, even anonymous".
Some of my scripts are API's returning just strings, the workaround for these is to use ContentService instead of HtmlService.
return ContentService.createTextOutput("Hello World");
Thank you for looking into this issue.
It looks like a problem at Google's end and they have acknowledged the bug as well. We'll have to wait until they issue fix.
Update: Looks like Google has rolled out an update and the issue is automatically resolved. The web app is now working as before.