I followed this topic community.getk2.org/forum/topics/i-imported-jcomment-to to import JComments to K2 Comments and it works well.
At the front-end the K2 Comments also works.

At the back-end of K2 Comments I got these 'notice' messages.

1. At the ‘Last Recorded IP’ column:
For Registered Users is it okay.
For Guest Users I got: Notice: Undefined property: stdClass::$commenterLastVisitIP in /home1/…/administrator/components/com_k2/views/comments/tmpl/default.php on line 174

2. At the ‘Flag As Spammer’ column:
For Registered Users I got: Notice: Undefined property: stdClass::$block in /home1/…/administrator/components/com_k2/views/comments/tmpl/default.php on line 181
For Guest Users it looks fine.

J! 2.5.3
JComments 2.3.0
K2 2.5.5

Any thoughts or suggestions are greatly appreciated?
Maybe it's just a cosmetic issue, please let me know?

Regards,
Marcel