Hello! I think it’s plugin’s bug.
An all day event on the first day of next month is displayed on the first day of current month in calendar view.
To fix this issue, we can modify get_events_between function in app/model/search.php from:
$spanning_string = 'i.end >= %d AND i.start <= %d ';
to:
$spanning_string = 'i.end >= %d AND i.start < %d ';
Thanks in advance, sorry for my bad english.