Emojis not displayed correctly

Hi there!

I just moved from DMSguestbook to your Plugin and like all the options a lot.

I just realized a bug displaying the emojis.
In the options I activated “BBcode and Emoji”. When I write an entry, I can choose an emoji.

But after submitting the entry, every emoji is just converted to ???? (4 question marks).

How can this bug be fixed?
Thank you in advance.

Regards,
Chipy

https://wordpress.org/plugins/gwolle-gb/