PHP error after upgrade to 3.0.2

After upgrading from OJS 2.4.8 to 3.0.2 I keep getting the following error in php_errors.log :

PHP Notice: unserialize(): Error at offset 312 of 317 bytes in /apps/ojs-3.0.2/lib/pkp/classes/db/ on line 347

Any ideas about what might be causing it?

I think I’ve seen mentioned somewhere that this is connected to the database encoding. Is there a change that it has changed or your does not have the right encoding selected?

Hello!! Finally they found the solution? I have exactly the same error when I run the upgrade.php for OJS 3.1.1-2. Thank you!