CodeIgniter 3.1.13 Upgrade Issues?

here are some suggestions on how to resolve the issues you are experiencing with CodeIgniter 3.1.13:

Set_flashdata function not working correctly for adding items to the cart

This issue could be caused by a number of factors, such as a problem with the way your sessions are being handled, a problem with the way your cookies are being set, or a problem with the way your cart data is being stored.

Here are some things you can check:

Make sure that you are setting the session.save_path directive in your PHP configuration file to a writable directory.
Make sure that your sessions are expiring after a reasonable amount of time. You can do this by setting the session.gc_maxlifetime directive in your PHP configuration file.
Make sure that your cookies are being set correctly. You can do this by checking the cookie_domain and cookie_path directives in your PHP configuration file.
Make sure that your cart data is being stored correctly. You can do this by checking the cart.storage setting in your CodeIgniter configuration file.
If you are still having problems, you can try using a different session driver, such as the Redis driver.

Having to re-login to the admin panel for it to function properly

This issue could be caused by a problem with the way your sessions are being handled or a problem with the way your cookies are being set.

Here are some things you can check:

Make sure that you are setting the session.save_path directive in your PHP configuration file to a writable directory.
Make sure that your sessions are expiring after a reasonable amount of time. You can do this by setting the session.gc_maxlifetime directive in your PHP configuration file.
Make sure that your cookies are being set correctly. You can do this by checking the cookie_domain and cookie_path directives in your PHP configuration file.
If you are still having problems, you can try using a different session driver, such as the Redis driver.

Problems seem to be related to session or cookie handling

Based on the two issues you are experiencing, it is likely that the problems are related to session or cookie handling.

Here are some general things you can check:

Make sure that you are setting the session.save_path directive in your PHP configuration file to a writable directory.
Make sure that your sessions are expiring after a reasonable amount of time. You can do this by setting the session.gc_maxlifetime directive in your PHP configuration file.
Make sure that your cookies are being set correctly. You can do this by checking the cookie_domain and cookie_path directives in your PHP configuration file.
Try using a different session driver, such as the Redis driver.
If you are still having problems, you can post a question on the CodeIgniter forum or contact the CodeIgniter development team for assistance.

I hope this helps!