This also happens when attempting to print in portrait mode... Just spoke with Adobe again (4th contact, I believe), and they are now saying this is a known bug.
I have been having the same problem for some time using an Epson Stylus Pro 4900 on a Mac Pro running High Sierra except that it has taken portrait format and turned it to landscape. This problem showed up when printing to real (expensive) paper as well as to printing to "Preview" on the screen.
I just seen an hour on the phone with a Level 2 Adobe person without a satisfactory resolution. However, he did point to the possibility of a printer driver update as being the answer. I think it is! On the Mac in System Preferences / Printers & Scanners, I removed my 4900 and then added it back. This updated the driver to driver 9.65 from 9.33.
Now the problem seems to have completely gone away. Landscape now prints in landscape; portrait prints in portrait. Exactly like it used to do. I hope this solves the problem for you too. Thank you for your efforts and for posting the problem.
I don't know how much this will help, but I saw a post by an Epson printing expert that suggests that there might be an interaction going on with macOS print presets. Part of his advice was to switch the Presets menu at the top of the Print dialog to Default, away from any macOS print presets you've saved. Below is the full link to his advice: