Hi!
If I mark my ground plane as "Infinite plane" it appears rotate 90 dgrs on the X-axis in the rendered viewport (The final render looks correct).
This has worked fine in previous versions. (I made a new file to be certain it wasn't anything weird in my project).
1 of 5 times I switch from solid to rendered view, it renders correctly (The other times I see the correct plane flash directly after the switch.