Having a weird situation with an internal app I developed using the JS API (currently pointing to v3.17). Anyways, our ArcGIS Server was at 10.2x and was recently upgraded to 10.41. Around that time, the ability of users to add new lines to a service enabled with feature access has failed.
The underlying JS code has not changed at all. Adding a point feature still works but, when attempting to commit a polyline, no error shows in the browser console but the Server log returns this:

The point feature service was published together with the line feature service and hasn't changed. Since the service hasn't changed, and the code of the application hasn't either, where should I start looking to determine why this is suddenly happening?
Steve