Here's link to a JPEG taken on an iPhone with the flash on that shows the problem on 2.7.7 and 2.7.8:
https://www.dropbox.com/s/52lq8gmj0e11l16/microbanding.JPG?dl=0
Be sure to view the JPEG at 1:1 to avoid any scaling artifacts.
I used PrintTool 1.1.0 on OS X Sierra, and 2.7.8 was printed with 2880 super, while 2.7.7 was printed with 2880. 2880 super was noticeably slower. The grey rectangle was made in Photoshop with L=25, so it should be the same as your 64/255 test.