If one attempts to add a note (using Gadget-ImageAnnotator) to an image on Commons one gets the error "Could not save your note (edit conflict or other problem). Please copy the text in the edit box below and insert it manually by editing this page." Despite there being no edit conflict.

See JavaScript here

Replicate:

1. Go to an image on Commons and click the Add note button below the image
2. Type test and click Save

Actual result: Error

Expected result: Note publishes to image and page reloads

macOS Chrome Version 77.0.3865.90 (Official Build) (64-bit)
Default skin
No console errors.