Answer

Windows maintains firewall settings for each application that is installed and each time a new version is installed, new permissions are created (usually when you run the new version for the first time). If the correct settings are not selected, this can result in the firewall will block traffic Designer needs to correctly operate and the new version may not detect devices such as Core's.

To confirm this, try turning off Windows firewall.

If devices now correctly appear, check the application permissions for each Q-Sys Designer instance listed in the firewall settings and apply the settings from the version that works to the one that doesn't.