When people use an interface of any kind for quite a period of time, what we might call muscle memory and eye brain hand coordination neural paths are established in the brain.
There is a lot of research out on this sort of stuff, worth checking out.
If an interface is suddenly changed it leads to some “pain” for many people, and that is partly what is being encountered here in their comments. It’s real.
When the interface is on a “personal” device, as part of a “personal” communication app, you are dealing with some quite deep things in the modern human experience.
Changing the GUI of an environment people perceive as part of their personal life is much more than just technical issues of app development as you might be gathering now
And the reactions that people will come forward with can be quite terse, they can reflect feelings you would normally only expect from something more obviously deeply personal in nature.
Some can even feel genuine trauma and angst. It makes our role as developers necessarily far more nuanced than just following our own good ideas at times.
A friend’s wife had some issues in her past, they expressed themselves by having the house furniture rearranged or even things utterly moved internally at random time intervals, so that when my mate came home, he never knew what was waiting for him, or for sure even where he would be sleeping!
Sometimes software GUI changes can feel to Users who rely on an app regularly, like having the very walls inside a house moved around on them, or going to get milk from the fridge and finding a washing machine there instead, or the TV is missing suddenly.
So a bit of heart for these kinds of things is needed by developers