I'm a tenant. My real estate agency uses a website through which you can, among other things, send them files. Including sensitive files, such as passport scans etc (often required in my country when you want to sign a lease).
The files are put inside a cache.
The cache is not secured and not even protected against directory listing in their web server. I can list the entire cache and see hundreds and hundreds of files there, including passport scans, salary certificates, etc. Wrote to them to tell them the issue existed and I wanted to talk to a person in charge of the website to disclose the details to them (I didn't want the details, including the URL, going back and forth in emails, knowing that they probably don't secure their emails correctly either).
The next day some lady calls me on my phone. She wouldn't understand the problem. "No Sir, in your personal account, you can only see YOUR documents, Sir." She was basically telling me what the correct behaviour would have been, completely unable to even process the idea that their website might be leaking highly sensitive documents in the wild.