I just tried to update from 2.22 (if I recall correctly) using online firmware upgrade button from the settings page, the device appeared to reboot as the light sequence changed and now I can no longer access the admin as binary is returned.
The curl output is expected. The html is gzip encoded, and since the supported browsers support that, there’s no plain-text version available. If you save it to a file and ungzip it, you should get a big html page.
It does look like PB is getting online, and is accessible. What do you get when you load it in a browser?
The firmware update process hashes the data, and then checks against a cryptographic signature, so it’s not likely to be corrupted in transit. Flash corruption is possible, but uncommon. Running the update again might clear that up.