In my experience with faults the apple service center can't be of any use at all. You have to speak to tech support over the phone as they have the ability to escalate. Once I got my issue escalated, I had someone work with me for literally weeks until it was resolved and one of the methods we used to get evidence for tech support was to video the instance where things disappeared. Tech support can also ask you to run a diagnostic check and send that file over to them for further analysis.
My problem was disappearing passwords from my iPhone and iPad although they stayed in place on my Mac.
I looked back at my notes for the issue I had with disappearing passwords and how I managed to detect the exact point that they disappeared from my iOS devices. The sequence was as follows:
- Can you have your MacBook and iPhone close together.
- Open them both at text replacement.
- Set auto-lock on iPhone to never: settings>display & brightness>auto-lock
- Do you have another phone or camera whereby you can take a video?
- Enter a couple of text replacement on your MacBook, see if it will appear on your iPhone?
- No worries if not, just shut down the Mac completely and power off.
- See if the text replacement appears on your iOS devices, hopefully it will?
- Sign out of iCloud on your iOS device and then back in again
- Whilst keeping the iOS device open and prevent auto-lock, start up your Mac
- Start filming and if possible have both screens in view on camera.
- Whilst logging into your Mac, keep eyes on your iOS device and hopefully you will witness the disappearance of text replacement.
- Wait until the text replacement disappears, so that you have it recorded on video.
- Providing this does actually happen as you expect, you then have filmed evidence.
Now of course I understand that this may not happen in the same way, but it might be worth doing it like that?
Note: if course I don't know your exact issue, I am not an engineer, I am sharing some ideas on how you might be able to get your issue resolved. Please ensure you always back up before signing out of iCloud. If my advice above doesn't resolve your issue or you are worried about further loss of data, please ignore it and speak to a professional tech support engineer at Apple, which is my first recommendation always.
Wishing you success and I hope it can get solved. I still haven't updated to iOS 15.
Michael