Upgrading to London is throwing message 'Illegal access to getter method getSource in class com.glide.sys.User' for all users logging on to instance
The instance must be having a custom Script includes for user redirection to other pages(like Service Portal, HR Portal etc.) which would be using unsupported functions. User can identify which Script Include is causing the error by going through the node logs. The most probable cause would that the script includes might contain gs object's internal elements which is locked down in London.
Refer below for supported functions to directly access the GlideUser
The script includes should use GlideRecord query instead of unsupported functions to evaluate the user criteria and redirect to other pages.