From further testing, I found this only occurs when performing an upgrade with the 'DistUpgradeViewNonInteractive' frontend.
The lock screen is inhibited during the upgrade, but seems to be re-enabled after the non-interactive upgrade. This isn't the case for a GUI upgrade.
From further testing, I found this only occurs when performing an upgrade with the 'DistUpgradeVie wNonInteractive ' frontend.
The lock screen is inhibited during the upgrade, but seems to be re-enabled after the non-interactive upgrade. This isn't the case for a GUI upgrade.