I am wondering why it is that the Forum app only works in one orientation, Apparently only such that my tablet buttons are on the bottom and keep getting hit turning off the tablet.
Surely there must be a simple widget that allows the presentation to rotate as the device is rotated. I only mention this as I am coming back from several such glitches as I was trying to post.
It rotates for me… Pixel C tablet.
Works rotated to either side on my Pixel2 phone but not upside down (vertical but with the power back on the top).
Media tech Tablet , Samsung Nook , and ZTE smartphone all have the issue, all other apps rotate.
Discourse (the forum software) doesn’t care about the orientation. However, most tablet and phone allow you to lock rotation to prevent the back & forth “glitches.” For example, I use the “mute” switch on my iPad to lock rotation while I’m watching videos, etc. Your experience may vary.
I have that and use it but the GF Forum does not as far as I can see
Are you using the Discourse App for iOS? If so, GF didn’t write it and doesn’t provide support for it.
If you open the forum with a browser, discourse is at the mercy of your browser and operating settings. Again, nothing that GF Support will be able to address.
Edited to add: In either case, you may find the Support community for Discourse to be helpful: https://meta.discourse.org Best of luck! 
This question is outside our team’s scope. I’ve moved it to the Everything Else so the discussion can continue there.