Ok, similar to the problem where saving metadata was not possible because of OpenAir plugin (see post After update to 3.1.2 the new submission not saved the metadata - #4 by Anuj_Mittal) i found out that here problem lies in ORCID plugin. After i disabled that plugin all works fine.
EDIT: i installed new version of ORCID plugin compatible with OJS 3.1.2 so i hope this will work now.
Regards.