First thing I would check is swiping down at the very top of your screen until the menu of being able to see the "quick settings menu" which will show the WiFi icon, Bluetooth, etc but look for the one labeled "portrait" (has padlock looking icon) and see if it's grayed out or of it's set to auto rotate. It may be rotating based on that but also depends on your camera setting for picture size of 3x4, 9x16, 1x1, full; possibly the 9x16 is causing it to rotate when you zoom? I very rarely use that size but I also have my screen locked so it doesn't auto rotate. After checking and changing anything and the issue still happens then what my next step would be is to get into the app info (hold down on the camera icon until a menu pops up above or below the camera icon) and click on the "i" in the upper right corner - scroll down until you see "storage" and you first try to to clear cache but most likely you'll need to clear the storage - keep in mind if you clear the storage of basically resets all settings from the app back to factory settings so any options you changed such as adding a watermark or location will need to be set up again. Restart the phone and hopefully that'll resolve it. When you restart hold down the volume down and the power button at the same time for roughly 5 seconds or until it restarts as that's a simple way to clear out a possible software glitch on any and all apps. They refer to that as a "soft reset" which I've used countless times over the years on phones for network connectivity issues or a glitchy app. Hope this helps
