Month not showing

Hi, I am using the plugin on my blog but it’s not working properly.
It seems like the name of the month isn’t displayed, instead there’s a number.

For example, for 2014 I see this:
2014 (90)
(24)
(19)
(33)

So it only shows the number of posts per month, but not the name of the month.

Any idea here? Thanks for your help!

https://ww.wp.xz.cn/plugins/collapsing-archives/