I have a theory that how those dead OBi100s come back to life.
Those (new) certificates are generated by Google Voice XMPP servers and they need to be registered on some CAs (certificate authorities).
When a client (OBi devices) tries to connect to a server (GV), the server will send back a certificate to the client. The client will first check roughly if it looks OK (i.e., expiration date, etc) and then turn to the stated CA in the certificate to check further. The CA must be in the trusted CA list the client has. If the CA says everything is fine then the connection happen. If any of the steps are not OK then the client will be "backing off".
So what could be wrong in the process? Could it be true that is GV's mistake that all those new certificates were "self-signed" and not went through the CA? Or GV regists those new certificate with a new CA that is not in the client's trusted CA list? Or some CA has DNS issue at the time of connection?
As long as the client (OBi device) stores a list of trusted CA, it doesn't seem the error from the client, rather the error from the server (GV server) or the CA. Once the error in the (GV) server or CA are corrected away, the client (OBi device) should connect to the server again without any software updates.
Say GV made a mistake by sending self-signed certificate to clients causing clients to "back off", OBiHai probably jumped in to change the firmware to accomodate the change by allowing self-signed certificate specifically from GV. That only happened to OBi2xx and above, not to OBi1xx.
Read about SSL/TLS below:
https://www.techrepublic.com/blog/data-center/ssl-tls-certificates-what-you-need-to-know/@SteveInWA could you ask GV and OBiHai what exactly happened?