Are you sure you signed in using the same account and on the same server ?
Did you check in Trash ?
You will of course have backup aia files for all your projects on your computer, so you could upload them as required if they really are all gone...
It wasn't deleted. It just inexplicably appeared in the directory. Previously, I had it placed in the directory. Essentially, I need to reorganize the categories. I have a lot of files and it would be very time-consuming to search through them one by one.
Can we ensure that such problems won't occur again in the future?
There are no such guarantees in life. Best to assume nothing and trust no-one, back up all your aia projects to computer, then back them up again somewhere else.