Garmin Montana 700i at software level 10.50. Display Orientation lock is not working. I have it set to auto and it worked before. Now there is no switching from portrait to landscape when I rotate the 700i.

Unable to duplicate with my 750i v1080.

You may need to perform a device reset.

Device reset did not change the behavior.  Probably shows that a setting is not causing the trouble.  I have had the 700i for about three weeks.  This behavior; not auto rotating started maybe a week ago.

I'm beginning to suspect something failed in the device.  I can no longer calibrate the compass. The first two steps (rotate and roll) work successfully; the third step (flip) fails every time.  I know it's not my doing; I was able to calibrate when I first got the device.

If I am correct this does not bode well for quality.  The Montana 700i was purchased the first week of December 2021.

Best to open a support ticket. This sounds like an issue with accelerometer in the device. You've already done a factory reset, which would have been my first suggestion for this problem as well.

There are things other than the accelerometer which enter into compass calibration. But not device rotation.

Spoke with Garmin support this morning.  Also did the full reset (press and hold power until red LED comes on, then release and double tap power) to no avail.  Since it is less than 30 days since delivery of the device Garmin had me go back to the store from which I ordered.  Initiated a return and replacement.  

FYI - The Montana 7x0 has been available to the public for nearly 16 months now, and has been in use for much longer (pre-release testing), and this is the *first* accelerometer hardware failure I have heard of. I am certain Garmin will be eager to examine the return. I am also certain your replacement will function as expected!