I experienced a weird behaviour with an XPages app this evening: it runs perfectly for a while and then suddenly it stopped with an error 500 "unresolved compilation error".
Server is V12, ODA ist the latest 11.something.
Using the template to update the app fixed the issue for a while - to be re-occurring after a bit.
What happens here?
Simple answer: the "client" opened the app on the server with a Domino Designer which does NOT have the plugins installed that the app is using. Due to DDE's "automatic build" feature enabled by default (and the "client" not being a developer) the app was then build - with errors.
Lessons learned: never let the "client" open the app with DDE if you do not know if everything is set up correctly
Thank you, Jesse, for the heads-up!