I just ran into this problem so I fixed it myself.
The issue is the get_recurrence_days() function in em-event.php is using a relative date which triggers this bug in php: https://bugs.php.net/bug.php?id=63863 which is present in 5.6 branch but not 7.
The fix is to simply add a line to the top of the setDate() function in em-datetime.php so it reads as follows:
public function setDate( $year, $month, $day ){
$this->modify('+0 day');
And then since the recurring events are generated when you save it you’ll probably have to go into each one and reschedule to a different date and then back again so they’re regenerated with the correct dates.
I don’t have a way to contact the developers directly, but hopefully someone can notify them so they can add fix this in a future version.
