The error code itself seems to have originated from the Spring Framework; they had the
420 code to indicate a
Method Failure, but Spring has since deprecated this code.
The Data Loader application is/was built using the Spring Framework, so it stands to reason that the error is coming from that somehow.
There is no direct confirmation or documentation from Salesforce about this error code, but they do have an open incident that matches the timeline, though it implies that the affected services are limited to Communities. (see attached photo)
I'm no stranger to Salesforce being cagey about widespread service disruption, and it seems that others have noticed that Salesforce has never really commented on this error in the past.
So for anyone else experiencing this issue at the same time as me, or in the future, hopefully this provides some kind of explanation / vindication.
After much back-&-forth with Salesforce Support, they ended up disabling the Salesforce Edge Network for our org.
Since then, we have experienced no further instances of
As of writing this, we have not been provided any explanation of this failure. We have a list of outstanding questions that we are pressuring them to answer, but we have yet to hear anything of substance from them.
Once we get any kind of details, I intend to update this post with more details for posterity & to be of more use for the community.