Some further diagnostics.
We host three tools on a retool.com instance. Two apps seem to be working fine. The third throws the Toaster error in edit mode. It does not throw the Toaster error in View mode, https://nsipesa.retool.com/app/matrix ; but it does throw it on https://nsipesa.retool.com/app/matrix?_releaseVersion=latest
Given that Did something change today? has also happened today, this suggests that it isn’t an isolated occurrence…