Thank you for answering my many questions, it was very helpful!
Reviewing this detail -- "Developers" which where allowed to see logs in 8.1, in 8.3 they could not see the logs but where authorized to login into the gateway. -- I wonder if in 8.1, Administrators and Developers were assigned to Status Page Permissions? With Administrators assigned to Gateway Config Permissions?
If this was the case, then after the upgrade, Administrators would be assigned to the new Gateway Write and Read Permissions. Due to the new webUI layout, the Status Page Permissions setting is no longer in 8.3 and you would not see the Developers level selected in the Roles & Permissions. Home Page Permissions migrated to Gateway Access Permissions and if this perm was left as its default setting of Public, you would be able to log into the Gateway with a Developers user, but be limited to seeing the Home section of the WebUI.
Info on 8.3 Roles/Perms: https://docs.inductiveautomation.com/docs/8.3/platform/security/gateway-general-security-settings#roles-and-permissions -- Update security tips (this is the info Michael referenced earlier in the thread) - https://docs.inductiveautomation.com/docs/8.3/getting-started/installing-and-upgrading/ignition-8-upgrade-guide/81to83-upgrade-guide#gateway-security
In this case, you could consider setting Developers to the Gateway Read Permissions setting to allow them to view the logs, but the Read permission gives read access to the general WebUI which would include configuration information, giving them different access than in 8.1.
I am working on updating the New in this Version section for the Roles/Perms changes -- https://docs.inductiveautomation.com/docs/8.3/new-in-this-version#security