Hi,
If you've updated your Community Builder and K2 components, you should also use the latest versions of their JoomSEF extensions - you can check if a new version is available on Manage Extensions page in JoomSEF.
As regards the JoomSEF update, if everything worked correctly and you didn't have any problems with your website, there wouldn't be a reason for updating. But since you experience some problems, you can try updating JoomSEF, maybe the problems were fixed in newer versions.
Of course, backup your website prior to updating any components, just in case something goes wrong.