This article provides a fix for when you try to log in to your Admin panel but the form just refreshes and you are unable to log in. This is because the Admin Session Size has been exceeded.
It is impossible to log in to the Admin, because the form keeps reloading.
The allowed session max size is exceeded.
var/log/support_report.log file for errors such as these:
[2023-07-13T04:26:09.792060+00:00] report.WARNING: Session size of 260572 exceeded allowed session max size of 256000.  
[2023-07-13T04:26:17.056714+00:00] report.WARNING: Session size of 260570 exceeded allowed session max size of 256000.  
If you see these errors, the solution would be:
Adobe Commerce on-premises:
Adobe Commerce on cloud infrastructure:
(This setting is only accessible in the Admin when the deployment/operation mode is default or developer. However, only the Production deployment mode is allowed in the Cloud environment.)
To increase this value, run this command in the terminal (SSH):
bin/magento config:set system/security/max_session_size_admin 500000
You can set to higher than 500000 depending on the existing max size reported in the error and you can also set the value to 0 to remove the session size limit.