Hi all. This actually happened to me before I read about the bug. I regularly share Samsung Health workout summaries with a friend of mine. It's always via WhatsApp, meaning that a copy of the photo is saved in my WhatsApp photos folder. Last week I got a text from a DIFFERENT friend asking "uh, why did you just send me a heart rate trace?" There was no record of this message being sent on my text thread with him in Samsung Messages, but when I saw him a week later he showed me his phone, and indeed I had sent a Samsung Health workout summary image to him.
This is downright scary. I don't have any "sensitive" photos on my phone, but if my boss randomly gets a photo of my wife or something, that's pretty awkward. I'm surprised Samsung isn't taking this more seriously. This is one of the worst data privacy issues I've ever seen in the tech world. The worst part is that you don't even know when a photo has been sent. I have no clue if Samsung Messages has sent my entire photo gallery to half the contacts in my phone.
Obviously, as soon as I read about this I disabled Samsung Messages and installed Android Messages. It doesn't support T-Mobile advanced messaging, which sucks. But it has a web interface, which is great.