This happens to every 1SE user occasionally, including us. It's not so much a bug but more an issue of the iPhone camera not registering the orientation of the device and quickly adjusting. It's annoying for sure. A quick way to see if the camera has adjusted orientation is to look where the time code is on the screen. If it's at the top, the camera was switched to landscape.
Rotate a Photo
Open up your Photos app to edit the image. Simply select the photo you want to edit and tap the rotate icon on the bottom. Once you have the perfect rotation, click done and you're ready to go.
Here's a quick article from Apple on using the Photos app.
Rotate a Video
A video is a little more complicated. You can use a 3rd party app like iMovie to make those adjustments. You can download iMovie for your iOS device here.
Here's a great article from Apple on how to use iMovie on your mobile device: Rotate or edit videos in iMovie.
We're actually working on an update to 1SE that lets folks rotate videos & photos within the app. This will be included in a much more robust editor for your content. We know it's needed and are working on getting it out there. Stay tuned.