Thanks for idea, however, I've tried to set it to both: ".mydomain.com" and "subdomain.mydomain.com" (this site is working as subdomain) and the result was the same: few session files were generated (for each page load), one of them contains actual session data but the next page after redirect does not see session data anymore.
I turned on full logging but can not see anything suspicious, session class is loading... where else I can look for issue?
INFO - 2018-05-22 08:36:48 --> Config Class Initialized
INFO - 2018-05-22 08:36:48 --> Hooks Class Initialized
DEBUG - 2018-05-22 08:36:48 --> UTF-8 Support Enabled
INFO - 2018-05-22 08:36:48 --> Utf8 Class Initialized
INFO - 2018-05-22 08:36:48 --> URI Class Initialized
INFO - 2018-05-22 08:36:48 --> Router Class Initialized
INFO - 2018-05-22 08:36:48 --> Output Class Initialized
INFO - 2018-05-22 08:36:48 --> Security Class Initialized
DEBUG - 2018-05-22 08:36:48 --> Global POST, GET and COOKIE data sanitized
INFO - 2018-05-22 08:36:48 --> Input Class Initialized
INFO - 2018-05-22 08:36:48 --> Language Class Initialized
INFO - 2018-05-22 08:36:48 --> Loader Class Initialized
INFO - 2018-05-22 08:36:48 --> Helper loaded: url_helper
INFO - 2018-05-22 08:36:48 --> Database Driver Class Initialized
INFO - 2018-05-22 08:36:48 --> Session: Class initialized using 'files' driver.
INFO - 2018-05-22 08:36:48 --> Controller Class Initialized
INFO - 2018-05-22 08:36:48 --> File loaded: /home/*******/login.php
INFO - 2018-05-22 08:36:48 --> Final output sent to browser
DEBUG - 2018-05-22 08:36:48 --> Total execution time: 0.0827
