Yes, I entered the SSID. I deleted the network info, re-entered, and many other tests. Gave up and retried a day later. Nothing worked until I broadcast the SSID.
About a week ago, it started working. I did not make any changes to the Uni, the network, or Wi-Fi router (SSID broadcast is disabled). The Uni firmware is still 1.7.0 (auto update is disabled.)
I have no idea why it works, but the device is untrustworthy.
Regardless, it seems downgrading the firmware is not possible if previous versions are unavailable.