A Microsoft file hosting and synchronization service.
Hello,
Just a quick heads up before we dive in, this is a public community forum staffed by regular users, we are not Microsoft employees or official support.
Since it keeps happening even with newly uploaded photos and your password is changed, I have a strong feeling another device connected to your account is silently syncing these deletions.
Do you have any other devices like an old phone, an iPad, or a second laptop that are still logged into this specific OneDrive account? A second device with a broken sync or aggressive local storage management could continuously tell the server to delete things, which then propagates to your computer and clears out your cloud.
Also, as a quick test, if you upload a single test picture directly through the OneDrive website using a web browser instead of using the sync app, does that photo still disappear the next day?
Let me know what other devices might have access so we can figure out exactly where these delete commands are coming from.