I have performed clean upgrade. All files except configuration file, file store folder and public folder were removed and than OJS 3.0.1 installed. I will copy .dat file in plugins/generic/usageStats and the results. Thanks.
As for stats data, they all are stored in usageEvent logs. They are processed by command, noted in Ubuntu cron, every 2 hours. Some of logs are then moved to /reject directory and others in the archive/ but all data are recorded in the database. I will check database once more and share with several lines.
If there is a need you can check link for the article, where stats data are not displayed. In articles, published before the upgrade, all is ok. The psychological distress and psychic phenomena in cancer patients during palliative care | Psychosomatic Medicine and General Practice