Previous/next month link is missing

Hey,

I installed the calendar on two websites. on one the previous/next month links are displayed: http://www.hlcmr.de/events (WP 4.3.1, calendar Version 3.12.6)

but on the not: http://www.hlci.de/events/ (WP 4.3, calendar version 3.12.3)

thanks for help!

https://ww.wp.xz.cn/plugins/the-events-calendar/