If you search by “Breaking Change” in this forum, you will find many!
On the past I developed the Title Links resolution for an important problem in ERPNext and frappe
After a period making it mature, one commit on the UI of the framework, completely and silently deprecated the JQuery widget that was being used to address the problem, using Awesomplete instead, what turned almost impossible at least to me maintain the app.
There’s other cases also, but or they are smaller or they dont resolve important features!