Seen on for example http://en.m.wikipedia.beta.wmflabs.org/wiki/Selenium_Edit_Test
As logged-in user with 'alpha' mode set, attempt to edit a page on beta labs.
VE never appears, Mobile user sees only a spinner.
VE seems to work correctly for non-Mobile user.
(Possibly related may be a recent change to Parsoid on beta labs https://bugzilla.wikimedia.org/show_bug.cgi?id=60694)
Version: unspecified
Severity: critical