next button only works when logged on wordpress..

Hi, i used this plugin on one of my friend’s website, I installed it using chrome and its working properly when I check it.. but then I tried different browsers then the problem occured.. homepage appears when you click the next button..

At first I thought that it was only a browser problem, but then i try to access the backend on the other browsers.. the next/previous button suddenly works.. Please help..

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