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WTH is this
Did you clear browser storage? This would explain it since it removes the encryption key from your device. If you didn't do that, I don't know how that happened, we would need to reproduce it first.
how do I sync them back?
To sync back, enter the passphrase again or reset in which case you get a new one that you need to enter on all of your devices.
(Background: desktop version of SN just decided to unconnect the NWC, and reconnecting it -- using exactly the same as used in phone, which works -- says "secret required")
With "reconnecting", do you mean you reconnected device sync by entering your passphrase or you tried to save NWC for sending again? "secret required" sounds like you tried to enter NWC credentials again and that the URL did not contain a "&secret=..." part. Are you sure it's there?
But I can see that there's an encrypted NWC wallet on the server for you, so you shouldn't need to enter NWC credentials again, only enter your passphrase in the screenshot you've shown me so your device can decrypt the wallet.