Description:
I have multiple sources, each of which is a board.

To reproduce the issue:
1. Go to Schedule Settings, select Line: Global, Grouping: None

Result:
"This view is only available if all teams are on the same schedule."

My teams are on the same schedule, they all started on 9 Feb, and all last 2 weeks.

I noticed that on the graphical schedule, the left boundary of the Epics (or Stories, it doesn't matter) of one of the teams, appears on 8 Feb, i.e. the day BEFORE they actually started the sprint. All the others are in line, slightly to the right, on 9 Feb, as I would expect.

Here are the start/end dates from the Sprint Report for the current sprint on all the projects.

Team 1: 09/Feb/16 10:31 AM - 23/Feb/16 10:31 AM
Team 2: 09/Feb/16 3:08 PM - 23/Feb/16 3:08 PM
Team 3: 09/Feb/16 2:48 PM - 23/Feb/16 2:48 PM
Team 4: 09/Feb/16 3:32 PM - 23/Feb/16 3:32 PM

Team 1 is the one that JPO is showing started on 8 Feb, and therefore probably why it thinks the teams are not on the same schedule.

Is there a date boundary issue? Note that I am in New Zealand. The above times are correct local times; JPO may be doing something funky when it tries to work out dates.