I did the upgrade to 3.0.1
When I started “Settings” to view the status of each my Folder Sync Connections, only one (out of 13) was present.
Just to be sure, in case a system reboot might help, I rebooted. Now two showed up.
I stopped Nextcloud-Client and restarted it. Now three Folders showed up.
Obviously, I repeated and got all 13 back.