After reading that you should modify the
session.gc_maxlifetime value to match1 the settings in:
Session Cookie Management→
Cookie Lifetime, and
Persistent Shopping Cart→
Persistence Lifetime (seconds)
I matched all the values to 31536000 seconds (365 days) and had our hosts change the GC value to match this. After the change was made, both front & backend login pages would simply redirect you to the login page after a successful login.
The only way I could resovle this was to revert the GC value back to it's original value (1440).
As soon as it was reverted, the problem was resolved.
I could find nothing in the error logs regarding this.