Why does ppp(8) lock up shortly after connection?
Prior to version 2.2.5 of FreeBSD, it was possible that your link was disabled shortly after connection due to ppp(8) mis-handling Predictor1 compression negotiation. This would only happen if both sides tried to negotiate different Compression Control Protocols (CCP). This problem is now corrected, but if you are still running an old version of ppp(8) the problem can be circumvented with the line
disable pred1