I clicked on the calendar page Home -> Calendar -> Month https://koha-community.org/calendar/action~month/ I see the entries for April. Now I click on May, for the next month. Nothing happens, I still see the April. I also tried from April 2017 and clicked back 11 month. No May 2016. I tried this with Firefox, Safari & Google Chrome. Same results, no May 2016
I can not reproduce the issue (calendar on https://koha-community.org/calendar/action~month/)
I can confirm the issue is now fixed, and the calendar works.
It did not work on May 23 but I cannot recreate now.